THE  PRINCIPLES  OF 

IRRIGATION  PRACTICE  ' 


BY 

JOHN  A.  WIDTSOE,  A.M.,  PH.D. 

PRESIDENT  OF  THE  UTAH  AGRICULTURAL  COLLEGE 


gorfe 
THE  MACMILLAN  COMPANY 

LONDON:  MACMILLAN  &  CO.,  LTD, 
1914 


c^ 

x^O   „ 


COPYRIGHT,  1914 
By  THE  MACMILLAN  COMPANY 

Set  up  and  electrotyped.    Published  August,  1914 


Mount  Pleasant  #re*« 

J.  Horace  McFarland  Company 
Harrisburg,  Pa. 


Brigham  Young.    (Born  1801;  died  1877.) 
The  founder  of  modern  irrigation  in  America. 


BY  THE  AUTHOR  TO  THE  MEMORY  OF  THE 
PIONEERS  WHO,  ON  JULY  24,  1847,  ENTERED  THE 
GREAT  SALT  LAKE  VALLEY,  AND  ON  THAT  DAY 
FOUNDED  MODERN  IRRIGATION  IN  AMERICA 


PREFACE 

IRRIGATION  and  dry-farming  are  rapidly  conquering 
drought.  By  these  twin  arts,  bountiful  and  regular 
harvests  may  be  gathered  in  the  humid  regions  during 
the  periodic  dry  seasons;  and  in  the  arid  regions,  the 
great  "deserts"  may  be  converted  into  most  fruitful  fields. 
Irrigation  has  a  splendid  record  of  success  from  the  begin- 
ning of  history;  dry-farming  has  only  in  recent  days 
extended  its  conquests  into  the  more  arid  regions;  both 
have  become  more  powerful  in  conquering  drought  as 
modern  science  has  been  applied  to  them. 

Successful  irrigation-farming  is  the  joint  product  of 
the  engineer  and  the  farmer.  To  the  engineer  is  given  the 
heavy  and  responsible  task  of  constructing  properly  a 
permanent  system  of  dams  and  canals  from  which  water 
may  be  drawn;  to  the  farmer  belongs  the  apparently 
humble  but  unending  and  difficult  task  of  using  the 
water  in  the  best  manner  for  crop-production.  Both 
workers  are  essential  for  success;  but,  the  work  of  the 
farmer  determines  the  permanence  and  extent  of  agricul- 
ture under  irrigation. 

Much  has  been  written  about  irrigation  for  the 
engineer,  but  little  for  the  farmer.  The  few  who  have 
written  about  farming  under  irrigation  have,  most  fre- 
quently, prepared  crop  or  soil  manuals,  in  which  the  use 
of  water  has  formed  a  minor  part.  This  book  is  an  attempt 
to  develop  the  principles,  so  far  as  present  knowledge  per- 
mits, upon  which  the  correct  use  of  water,  by  the  farmer, 

(ix) 


X  PREFACE 

must  rest.  Crop  or  soil  treatments  which  are  not  con- 
nected directly  with  the  use  of  water  are  not  discussed  or 
are  greatly  subordinated.  The  various  aspects  of  the 
complex  art  of  irrigation — agricultural,  economic,  social 
and  legal — will  some  day  receive  separate  and  special 
treatment;  in  this  volume  one  line  of  thought  only  has 
been  followed — the  correct  use  of  water  in  irrigation. 

The  aim  of  this  book  is  to  furnish  to  students  and 
intelligent  farmers  a  modern  view  of  the  principles  of 
irrigation  practice.  Simple  language  has  been  used  and 
unnecessary  technical  terms  have  been  avoided.  Obvious 
matters,  and  those  which  vary  with  local  conditions  and 
must  therefore  be  learned  by  experience,  have  been 
eliminated.  The  beginner  in  irrigation  has  been  kept  in 
mind;  but  the  book  is  essentially  a  manual  for  those  who, 
whether  in  arid  or  humid  climates,  having  cast  their  lots 
with  irrigation,  desire  mastery  of  their  work  by  an  intel- 
ligent comprehension  of  the  natural  laws  involved  in 
irrigation-farming.  The  actual  handling  of  water  can  be 
learned  only  by  experience — that  is  the  beginner's  heavy 
lesson;  the  refinements  of  irrigation,  by  which  its  success 
at  last  is  measured,  come  later,  and  are  unknown  to 
many.  The  man  who  lives  year  after  year  under  the 
ditch,  and  raises  his  family  there,  needs  as  much  if  not 
more  help  than  the  pioneer  whose  chief  sorrow  is  the 
aggravating  self-will  of  the  water  as  it  flows  over  the 
newly  broken  land. 

Some  subjects  have  been  touched  on  lightly  in  this 
volume  because  they  are  more  fully  developed  in  the 
author's  book  on  ''Dry-Farming."  In  fact,  that  book 
and  this  one  are  a  continued  study  of  the  water  factor  in 
agriculture — perhaps  the  most  important  of  the  physical 
factors.  Schools  of  agriculture,  whether  in  arid  or  humid 


PREFACE  xi 

regions,  might  profitably  organize  classes  in  this  subject. 
Classes  in  fertilizers  and  related  subjects  are  taught  as 
a  matter  of  course,  but  the  water  factor,  of  greater  impor- 
tance, is  given  incidental  mention  in  courses  on  soils  or 
plant  physiology.  At  the  Utah  Agricultural  College  it  has 
been  found  satisfactory  to  give  a  half-year  course  in  dry- 
farming,  followed  by  a  half-year  course  in  irrigation 
practice,  the  two  courses  constituting  a  year's  study  of 
the  water  factor  in  agriculture. 

The  irrigation  literature  of  the  world  has  been  quite 
fully  examined  in  the  preparation  of  this  book;  but,  since 
the  work  has  been  done  far  from  large  libraries,  many 
important  papers  have  been  inaccessible.  However,  as  a 
possible  compensating  condition,  the  work  has  been  done 
within  hearing  of  the  ripple  of  the  irrigation  ditch,  in 
the  heart  of  the  irrigated  section.  Free  use  has  been  made 
of  all  available  information,  but  of  especial  help  have 
been  the  magnificent  series  of  irrigation  bulletins  issued 
by  the  Irrigation  Investigations  of  the  Office  of  Experi- 
ment Stations  of  the  United  States  Department  of  Agri- 
culture. The  splendid  work  of  the  Bureau  of  Soils  of  the 
United  States  Department  of  Agriculture  has  also  been 
of  the  greatest  assistance.  It  is  a  pity  that  the  heated  dis- 
cussion of  a  theory  should  overshadow  this  vast,  accurate 
and  remarkable  soil  work,  the  like  of  which,  issuing  from 
one  institution,  is  not  to  be  found. 

At  the  end  of  each  chapter  has  been  placed  a  short 
list  of  references  for  the  use  of  those  who  desire  to  carry 
their  studies  further.  Care  has  been  taken,  except  in 
two  or  three  instances,  to  suggest  only  such  materials  as 
are  readily  available.  These  references  would  make  a 
very  good  working  library  on  irrigation  and  may  be 
obtained  at  a  slight  cost.  In  Appendix  C  is  given  a  brief 


xii  PREFACE 

list  of  books  on  irrigation.   No  attempt  is  made  to  supply 
in  this  volume  a  complete  bibliography  of  irrigation. 

To  friends  and  colleagues  in  many  parts  of  the  world 
hearty  thanks  are  offered  for  valuable  help  rendered  in 
the  preparation  of  this  book.  My  Utah  colleagues,  many 
of  whom  have  been  connected  with  the  long  experimental 
study  of  irrigation  at  the  Utah  Station,  have  given  freely 
of  their  time  and  information  to  make  the  book  accurate 
and  worthy  of  the  cause.  I  am  under  particular  obliga- 
tion to  Dr.  Robert  Stewart,  Dr.  F.  S.  Harris,  Prof.  W.  W. 
McLaughlin  and  Prof.  L.  A.  Merrill,  and  to  Librarian 
Elizabeth  C.  Smith,  who  has  kindly  gathered  irrigation 
literature  from  all  parts  of  the  world.  My  brother,  Prof. 
O.  J.  P.  Widtsoe,  has  in  many  ways  given  most  valuable 
help.  If  this  book  and  its  companion  volume  shall  be  of 
service,  the  first  credit  belongs  to  Dr.  L.  H.  Bailey,  the 
Editor  of  the  Rural  Series  of  books,  through  whose  wise 
and  kindly  urging  these  books  were  written,  and  the  many 
others,  by  other  hands,  which  have  made  available  to 
humanity  the  great  applications  of  modern  science  to 
rural  problems. 

JOHN  A.  WIDTSOE. 

LOGAN,  UTAH. 


NOTE. — Unless  otherwise  stated,  wherever 
"inch"  or  "foot"  of  water  is  used  in  this  book 
it  refers  to  the  depth  to  which  the  water  would 
cover  the  ground. 


TABLE   OF  CONTENTS 

A.  INTRODUCTION 
CHAPTER  I 

PAGES 

THE  MEANING  OF  IRRIGATION 1-7 

Annual  rainfall,  1 — Seasonal  rainfall,  2 — Variations  in 
rainfall,  2 — Conservation  of  rainfall  on  farms,  3 — Condi- 
tions of  dry-farming,  3 — Conditions  of  irrigation,  4 — 
Irrigation  defined,  4 — Geographical  need  of  irrigation,  5 
— Possible  extent  of  irrigation,  5 — Mission  of  irrigation 
and  dry-farming,  7. 

B.   THE  RELATION  OF  WATER   TO  SOILS 

CHAPTER  II 

SOIL  MOISTURE 8-20 

Attraction  between  near  bodies,  8 — Soil  particles,  9 — 
The  soil-moisture  film,  11 — Thickness  of  film  and  diame- 
ter of  particles,  12 — Hygroscopic  coefficient,  13 — The 
wilting  coefficient,  14 — Lento-capillary  point,  16 — 
Maximum  capillary  capacity,  17 — Free  water,  17— 
Summary,  19. 

CHAPTER  III 

THE  SOIL  AS  WATER  RESERVOIR 21-39 

Irrigated  soils  are  unsaturated,  22 — The  movement  of  soil 
moisture,  23 — The  distribution  of  soil  moisture,  25 — 
Field  moisture  capacity,  29 — Water  distribution  in 
furrow  irrigation,  30 — Effect  of  hardpan^  32— Effect  of 
gravel,  34 — Water  table  near  surfaceTsJ^Soil  treatment, 
35 — How  much  water  can  be  stored,  35 — Absorption  of 
water  by  soils,  38. 

(xiii) 


xiv  TABLE  OF  CONTENTS 

CHAPTER  IV 

PAGES 

SAVING  WATER  BY  CULTIVATION 40-63 

The  run-off,  40 — The  upward  movement  of  water,  42 — 
Intensity  of  evaporation,  44 — Conditions  determining 
evaporation,  46 — Mulching  to  check  evaporation,  49 — 
Self-mulching  soils,  52— Time  of  cultivation,  53 — 
Depth  of  cultivation,  55 — Frequency  of  cultivation,  58 — 
Cultivation  and  soil  fertility,  59— Rolling,  62. 

CHAPTER  V 

SOIL  CHANGES  DUE  TO  IRRIGATION  WATER     ....     64-107 

Contraction  and  moisture  film,  64 — Cohesion  of  soil 
particles,  65 — Volume  changes  of  soils,  67 — Effect  on  top 
soil,  69 — Successive  wetting  and  drying,  70 — Natural 
packing  of  soil,  70 — Soil  temperature,  71 — Water  a 
universal  solvent,  72 — Humid  and  arid  soils  contrasted, 
73 — Continuous  solubility  of  soils,  74 — Absorption  by 
soils,  76 — Composition  of  drainage  water,  78 — Concen- 
tration of  soil  moisture,  79 — Loss  by  drainage,  79 — 
Upward  leaching,  81 — Salinity  of  river  waters,  82 — 
Salinity  of  lake  waters,  86 — Salinity  of  mineral  springs, 
86 — Soil  moisture  and  natural  waters  compared,  87 — 
Ash  constitutents  added  by  irrigation  water,  87 — Use  of 
concentrated  waters,  89 — Need  of  water  surveys,  90— 
Composition  of  natural  waters,  90 — Classification  of 
natural  waters,  92 — Plant-food  value  of  irrigation 
water,  93 — Suspended  matter  in  river  water,  95 — Sea- 
sonal variation  of  suspended  matter,  98 — Suspended 
matter  added  to  soil  by  irrigation,  100 — Suspended 
matter  derived  from  surface  soils,  100 — Composition  of 
river  sediments,  101 — Physical  effects  of  sediments, 
102 — Cultural  treatment  of  sediments,  103— Effect  of 
sediments  on  crop-yields,  104  —  Water  and  soil  life, 
104. 


TABLE  OF  CONTENTS  XV 

C.   THE  RELATION  OF  WATER   TO  PLANTS 

CHAPTER  VI 

PAGES 

CONDITIONS  DETERMINING  THE  USE  OF  SOIL  MOISTURE  BY 

PLANTS '. 108-126 

Absorption  of  water  by  roots,  109 — Transpiration,  110 — 
The  initial  percentage  of  soil  moisture,  111 — Distribution 
of  water  in  the  soil,  114— The  effect  of  time,  115 — The 
depth  of  soil,  116 — Physical  composition  of  soils,  117 — 
Chemical  compositions  of  soils,  118 — Plowing,  120 — 
Cultivation,  121 — Manuring,  121 — Vigor  of  plant,  121 — 
Root-system,  122 — Age  of  plants,  122 — The  kind  of  crop, 
123 — The  seasons,  124. 

CHAPTER  VII 

THE  WATER-COST  OF  DRY  MATTER     .    • 127-157 

Carbon-assimilation,  128 — Plant  age  and  carbon-assimi- 
lation, 129 — Conditions  of  growth,  130 — The  transpira- 
tion ratio,  131 — The  seasons,  136 — The  soil,  137 — 
Mineral  food  or  soil  fertility,  139 — Cultural  operations, 
141 — The  vigor  of  the  plant,  143 — Varying  quantities 
of  water,  144 — Maximum  yield  with  given  quantity  of 
water,  151 — The  nature  of  the  crop,  154 — Summary,  155. 

CHAPTER  VIII 

CROP  DEVELOPMENT  UNDER  IRRIGATION 158-172 

Response  to  irrigation,  159 — Proportion  of  roots,  160 — 
Proportion  of  leaves  and  stems,  163 — Proportion  of  heads 
and  grain,  166 — Other  plant  parts,  169. 


xvi  TABLE  OF  CONTENTS 

CHAPTER  IX 

PAGES 

THE  TIME  OF  IRRIGATION 173-188 

The  ideal  principle,  173 — Fall  irrigation,  175 — Winter 
irrigation,  178 — Early  spring  irrigation,  181 — Irrigation 
during  growth,  182 — Time  of  irrigating  short-season 
crops,  183 — Time  of  irrigating  long-season  crops,  184 — 
Night  versus  day  irrigation,  187. 

CHAPTER  X 

THE  METHOD  OF  IRRIGATION 189-215 

Sub-surface  irrigation,  189 — Surface  irrigation,  193 — 
Permanent  ditches,  196 — Field-ditch  or  field-lateral 
method,  198— The  border  method,  202— The  check 
method,  202 — The  basin  method,  207 — The  furrow 
method,  207— Summary,  214. 

CHAPTER  XI 

CROP  COMPOSITION 216-230 

Groups  of  plant  constitutents,  217— Water,  217 — Ash, 
219— Protein,  220— Fat,  223— Carbohydrates,  224— 
Sugars,  224 — Starch,  226— Woodiness,  226 — Color  and 
flavor,  227 — Flour,  227— Cooking  value,  228— Effect 
of  cultural  treatment,  228. 

D.   CROPS    UNDER  IRRIGATION 

CHAPTER  XII 

THE  USE  OF  THE  RAINFALL 231-239 

Irrigation  supplementary  to  rainfall,  231 — Crop-pro- 
ducing power  of  rainfall,  232 — Results  of  dry-farming, 
233 — Crop  value  of  rainfall  in  irrigation,  233 — Conserv- 
ing the  rainfall,  235 — Distribution  of  rainfall,  235 — 
Storing  water  in  the  soil,  236 — Cultivation,  237 — Pro- 
portion of  rainfall  conserved,  237 — Relation  of  irriga- 
tion and  dry-farming,  237 — Dry-farm  homesteads,  238. 


TABLE  OF  CONTENTS  xvii 

CHAPTER  XIII 

PAGES 

IRRIGATION  OF  CEREALS 240-265 

Spring  vs.  fall  wheat,  241 — Quantity  of  wheat  to  sow, 
241 — Method  of  sowing  wheat,  242 — Cultivation  of 
wheat,  243— Method  of  irrigating  wheat,  243 — Time  to 
irrigate  wheat,  246 — Quantity  of  water  for  wheat,  248 — 
Oats,  253— Barley,  255— Rye,  255— Corn,  255— Time 
to  irrigate  corn,  258 — Quantity  of  water  for  corn,  259 — 
Rice,  262. 

CHAPTER  XIV 

ALFALFA  AND  OTHER  FORAGE  CROPS  AND  PASTURES  .  266-285 
Alfalfa  or  lucern,  266— Cultivation  of  alfalfa,  268— 
Method  of  irrigating  alfalfa,  269 — Time  to  irrigate  alfalfa, 
270 — Quantity  of  water  for  alfalfa,  274 — Alfalfa  seed,  277 
— Hay-making  crops,  278 — Red  clover,  281 — Pastures 
and  meadows,  281. 

CHAPTER  XV 

SUGAR  BEETS,  POTATOES  AND  MISCELLANEOUS  CROPS  .  286-313 
Sugar  beets,  286 — Method  of  irrigating  sugar  beets,  289 
—Time  to  irrigate  sugar  beets,  290 — Quantity  of  water 
for  beets,  293 — Carrots,  296 — Other  root  crops,  297— 
Potatoes,  298 — Peas  and  beans,  301 — Fiber  crops,  305 — 
Hops,  306 — Tomatoes,  cantaloupes,  etc.,  306 — Cab- 
bage, cauliflower,  etc.,  308 — Asparagus  and  celery,  309 — 
Onions  and  miscellaneous  crops,  310. 

CHAPTER  XVI 

FRUIT  TREES,  OTHER  TREES  AND  SHRUBS  ....  314-330 
Fruit-growing,  314 — Method  of  orchard  irrigation,  315 — 
Time  of  orchard  irrigation,  319 — Quantity  of  water  for 
orchards,  322 — Other  conditions  of  orchard  irrigation, 
323— Nursery  stock,  326— Small  fruits,  326— Grape- 
vines, 327 — Plants  for  ornament  and  comfort,  328. 


xvni  TABLE  OF  CONTENTS 

E.   MISCELLANEOUS 
CHAPTER  XVII 

PAGES 

THE  DUTY,  MEASUREMENT  AND  DIVISION  OF  WATER  .     331-370 

The  duty  of  water,  331— Classes  of  duty,  334 — Deter- 
mination of  duty  of  water,  difficult,  336 — Duty  of  water 
in  Africa,  338— Duty  of  water  in  Asia,  339— Duty  of 
water  in  Europe,  341 — Duty  of  water  in  South  America, 
342 — Duty  of  water  in  Australia,  343 — Duty  of  water  in 
North  America,  343 — Bear  River  Canal  experience,  344 — 
Idaho  results,  345 — Miscellaneous  results,  345 — The 
Utah  results,  346 — Need  of  measuring  water,  347 — Who 
shall  measure  the  water?  349 — Classes  of  measurement, 
349 — The  Cippoletti  weir,  353 — Divisors,  355 — Mean- 
ing of  the  distribution  of  water,  357 — Methods  of  Dis- 
tribution, 358 — Continuous  flow,  358 — Continuous 
rotation,  361— Distribution  on  application,  364 — Organi- 
zation for  distribution,  365 — Regulations  and  records, 
368. 

CHAPTER  XVIII 

OVER-IRRIGATION  AND  ALKALI 371-405 

Seepage  from  reservoirs  and  canals,  371 — Loss  from 
excessive  irrigation,  373 — Ground  water,  374 — Com- 
parison with  humid  areas,  375 — Lined  ditches — a  rem- 
edy, 376 — The  economical  use  of  water — a  remedy,  381 — 
Drainage — the  final  remedy,  381 — Alkali  defined,  383 — 
Seepage  and  alkali,  384 — Upward  leaching,  385 — Use  of 
saline  water,  387 — Alkali  deposits,  388 — Kinds  of  alkali, 
390 — Tolerance  for  alkali,  392 — Cropping  against 
alkali,  397 — Chemical  treatment  for  alkali,  398 — Scra- 
ping the  surface,  399 — Tillage  against  alkali,  399— Wash- 
ing out  alkali,  400 — Underdrainage — the  final  remedy, 
400. 


TABLE  OF  CONTENTS  xix 

CHAPTER  XIX 

PAGES 

IRRIGATION  IN  HUMID  CLIMATES 406-418 

Dry  seasons,  407 — Results  of  irrigation  in  humid 
regions,  409 — Methods  of  applying  water,  412 — The  duty 
of  water,  413 — Sources  of  water,  413 — Water-conserva- 
tion methods,  414 — Value  of  sewage  water,  414 — The 
use  of  sewage,  415 — Factory  and  mill  waste,  417. 

CHAPTER  XX 

IRRIGATION  TOOLS  AND  DEVICES 419-444 

Clearing  and  breaking  the  land,  419 — Laying-out  the 
farm,  420 — Leveling  the  land,  423 — Making  farm 
ditches,  426 — Gates  and  checks,  434 — Ridging  and  fur- 
rowing, 439 — Mulching  the  soil,  440 — Measuring  the  flow 
of  water,  441. 

CHAPTER  XXI 

THE  HISTORY  OF  IRRIGATION 445-471 

The  antiquity  of  irrigation,  445 — The  Christian  era  to 
1800,  449 — Irrigation  in  recent  times,  451 — The  found- 
ing of  modern  irrigation  in  America,  454 — The  growth  of 
American  irrigation,  457 — The  Union  Colony  of  Colorado, 
460 — The  United  States  Reclamation  Service,  461 — 
The  United  States  Department  of  Agriculture,  464 — 
The  experiment  stations,  466 — The  Irrigation  Con- 
gress, 470. 

CHAPTER  XXII 

PERMANENT  AGRICULTURE  UNDER  IRRIGATION  .  .  .  472-476 
The  big  irrigation  problem,  472 — The  spirit  of  irrigation, 
473 — No  essential  difference  between  irrigation-  and 
humid-farming,  473 — History  assures  permanence  of 
irrigation,  474 — The  question  of  plant-food,  474 — Some 
advantages  of  irrigation,  476 — Finally,  476. 


XX  TABLE  OF  CONTENTS 

APPENDIX 

PAGES 

A.  WATER  CONSTANTS 477 

B.  DISCHARGE  OVER  CIPPOLETTI'S  WEIR 478-483 

C.  LIST  OF  AMERICAN  BOOKS  ON  IRRIGATION      .      .      .  484 

INDEX  485-496 


LIST  OF  ILLUSTRATIONS 

FIG.  Page 

Brigham  Young Frontispiece 

1 .  Progressive  averages  of  annual  rainfall 3 

2.  The  limited  water  supply  makes  it  unlikely  that  more  than  one- 

tenth  of  the  land  will  be  irrigated 5 

3.  The  value  of  water  in  an  arid  land 6 

4.  Soil  is  a  mixture  of  particles  of  very  varying  size 10 

5.  The  moisture  film  surrounding  a  soil  particle 18 

6.  Flooding  new  land 24 

7.  Distribution  of  water  in  soil  immediately  after  an  irrigation.  ...  27 

8.  Distribution  of  water  in  soil  under  furrow  irrigation 31 

9.  Penetration  of  roots  of  prune  tree 36 

10.  Evaporation  usually  exceeds  rainfall 44 

11.  Relation  between  temperature  and  evaporation 48 

12.  Evaporation  losses  from  soils  protected  with  mulches  of  differ- 

ent depths 51 

13.  Orchard  well  cultivated  to  prevent  evaporation 57 

14.  Mulching  the  garden  with  a  hand  cultivator 61 

15.  Adhesion  of  hairs  due  to  water 65 

16.  Cracked  river  sediments  showing  volume  changes  due  to  water  68 

17.  Midsummer  snow  in  the  tops  of  the  mountains 75 

18.  Badly  corroded  ditch  due  to  excessive  fall 95 

19.  Walled  ditch  to  prevent  erosion  of  easily  "washed"  soil 97 

20.  Daily  discharge  of  Malheur  River 99 

21.  Daily  discarge  of  Mackenzie  River 99 

22.  Deposit  in  field  of  suspended  matter  from  irrigation  water 102 

23.  Stomatal  apparatus  in  carnation  leaf 132 

24.  Determining  the  transpiration  ratio 135 

25.  Yield  of  dry  matter  of  cereals  with  varying  quantities  of  water.  .  149 

26.  Yield  of  dry  matter  of  cereals  per  inch  of  irrigation  water 149 

27.  Crop-producing  power  of  30  acre-inches  (wheat) 152 

28.  Crop-producing  power  of  30  acre-inches  (alfalfa) 152 

29.  Crop-producing  power  of  30  acre-inches  (sugar  beets) 153 

30.  Effect  of  little,  medium  and  much  water  on  wheat 160 

31.  Proportion  of  grain  and  straw  with  varying  irrigations 168 

32.  Plan  of  a  sub-irrigated  farm 191 

33.  Lee's  sub-irrigation  system 192 

(xxi) 


xxii  LIST  OF  ILLUSTRATIONS 

FIG.                             v  Page 

34.  A  permanent  ditch  in  an  orange  grove 196 

35.  Plan  of  field-ditch  irrigation 197 

36.  Flooding  from  ditches  running  down  the  steepest  slope 198 

37.  Flooding  from  field  ditch 198 

38.  Flooding  with  aid  of  canvas  dam " 199 

39.  Laterals  made  in  field  and  dammed  with  small  piles  of  manure 

for  next  year's  irrigation 200 

40.  Plan  for  border  irrigation 201 

41.  Border  method  of  irrigation 202 

42.  Irrigating  cherries  under  check  system 203 

43.  Rectangular  check  method  of  irrigation 204 

44.  Contour  check  method  of  irrigation 205 

45.  Filling  checks  with  detachable  pipes. 206 

46.  Orchard  irrigation  by  basin  method 207 

47.  Orchard  irrigation  by  basin  method 207 

48.  Grading  of  interior  of  basins  to  prevent  water  from  coming  in 

contact  with  trees 208 

49.  Furrow  irrigation 208 

50.  Furrow  irrigation  of  young  alfalfa 209 

51.  One-way  furrow  irrigation 210 

52.  Furrowing  land 211 

53.  Standpipe  supplying  furrows  with  water 212 

54.  Zigzag  furrows  to  insure  uniform  distribution  over  soil 213 

55.  Another  type  of  zigzag  furrows 214 

56.  Lath-box  for  distributing  water  to  furrows  from  head  ditch. .  .  .  214 

57.  Yield  of  crops  due  to  rainfall 235 

58.  Irrigating  wheat 244 

59.  Canvas  dam  to  check  water 245 

60.  Irrigated  wheat 249 

61.  Irrigated  oats 251 

62.  Plan  of  rice  irrigation 254 

63.  Yield  vs.  water  (wheat) 256 

64.  Producing  power  of  30  acre-inches 257 

65.  Yield  vs.  water  (corn) 261 

66.  Irrigated  corn  in  Arizona 262 

67.  Plan  of  irrigating  an  alfalfa  field 270 

68.  Temporary  county  fair  building  constructed  of  baled  alfalfa  hay  271 

69.  An  alfalfa  field  in  Nevada 272 

70.  Yield  vs.  water  (alfalfa) 276 

71.  Flooding  pasture  land 280 

72.  Irrigating  young  alfalfa 281 

73.  Irrigated  cane  in  Kansas 283 

74.  A  sugar  beet  field 287 


LIST  OF  ILLUSTRATIONS  xxiii 

FIG.  Page 

75.  Loading  sugar  beets  in  factory  bins 288 

76.  Irrigating  potatoes 293 

77.  Yield  vs.  water  (sugar  beets) 295 

78.  Plan  of  potato  irrigation 298 

79.  Irrigating  potatoes 299 

80.  Irrigated  field  peas 302 

81.  Irrigated  celery 304 

82.  Irrigated  pumpkins 305 

83.  Irrigated  onions 307 

84.  Yield  vs.  water  (potatoes) 309 

8c.  Irrigated  Egyptian  cotton 311 

86.  Irrigating  cantaloupes 312 

87.  Irrigating  an  apple  orchard , 318 

88.  On  the  upper  canal 322 

89.  An  irrigated  prune  orchard .  .• 325 

90.  An  irrigated  date  palm  orchard 328 

91.  Canal  crossing  river  in  an  inverted  syphon 332 

92.  Looking  down  the  Bear  River  Canal 333 

93.  Lateral  outtake  from  large  canal 335 

94.  Headgate  of  a  canal 340 

95.  A  cable  measuring  station  with  automatic  gauge 348 

96.  Lyman  rectangular  weir 350 

97.  Longitudinal  section  of  Lyman's  weir 351 

98.  Cippoletti  weir 353 

99.  Details  of  Cippoletti  weir 354 

100.  Scale  to  be  screwed  on  side  of  Cippoletti  weir 355 

101.  Divisor  attached  to  Cippoletti  weir 356 

102.  Turnout  and  measuring  weir 357 

103.  Device  for  diverting  a  constant  quantity  of  water 357 

104.  The  need  of  storing  water  in  reservoirs 359 

105.  Rise  of  ground  water  from  irrigation 374 

106.  Chain  puddler.    Used  in  making  canals  watertight 376 

107.  Modified  chain  puddler 377 

108.  \\  ooden  stave  pipe  carrying  irrigation  water 378 

109.  Lateral  lined  with  concrete .s 379 

1 10.  Cement-lined  main  canal 380 

111.  Pumping  plant 382 

112.  Drainage  of  irrigated  lands  by  intercepting  drains 383 

113.  Structure  of  an  alkali  spot 386 

114.  Quaternary  Lakes  of  the  Great  Basin.  Sources  of  alkali  deposits.  389 

115.  Effect  of  a  strong  solution  of  potassium  nitrate  on  protoplasm.  392 

1 16.  Vegetation  on  alkali  lands 393 

117.  Alkali  rising  in  spots  on  irrigated  pasture 396 


xxiv  LIST  OF  ILLUSTRATIONS 

FIG.  Page 

118.  The  annual  rainfall  of  Milan  compared  with  that  of  humid  and 

arid  districts  in  the  United  States 408 

119.  Comparative  yields  of  strawberries,  irrigated  and  unirrigated  409 

120.  An  irrigation  plant  in  Pennsylvania 412 

121.  Distribution  of  water  on  Craigentinny  Meadows,  Edinburgh. .   416 

122.  Section  of  cement  flume 420 

123.  Section  of  V-shaped  flume 420 

124.  Wooden  flume 420 

125.  Section  of  rectangular  flume 420 

126.  Flume  with  lateral  gate 421 

127.  Buck  scraper 421 

128.  Leveler  or  float 422 

129.  Shuart  grader 422 

130.  Soil  auger 423 

131.  Lateral  plow 423 

132.  V-crowder 424 

133.  Building  a  ditch 424 

134.  Typical  forms  of  farm  ditches 425 

135.  Concrete  drop  in  ditch 426 

136.  Drop  in  flume 427 

137.  Distributor  for  hose 428 

138.  Attaching  hose  to  distributor. , 428 

139.  Leveling  device 428 

140.  Lateral  headgate 429 

141.  Concrete  gate 429 

142.  Dammer 429 

143.  Board  dam 429 

144.  Canvas  dam 430 

145.  Canvas  dam  with  opening 430 

146.  Metal  dam 430 

147.  Distribution  of  water  from  flume  to  furrows 430 

148.  Distribution  through  wooden  tubes 430 

149.  Lath  check 431 

150.  Conducting  water  down  inclines  in  concrete  pipes 431 

151.  Roller  furrower 432 

152.  Utah  lay-off  and  pulverizer 434 

153.  Robinson's  adjustable  corrugator  and  renovator 434 

154.  Ridger  in  check  and  basin  irrigation 435 

155.  Ridger  in  check  and  basin  irrigation 435 

156.  Furrower  in  action 435 

157.  Cultivator 436 

158.  Cultivator  attachments 436 

159.  Beet  cultivator  attachments 437 


LIST  OF  ILLUSTRATIONS  xxv 

FIG.  Page 

160.  Alfalfa  renovator 438 

161.  Clod  crusher,  pulverizer,  leveler  and  smoother 438 

162.  Frieze  water  register 439 

163.  Device  for  measuring  miner's  inches 440 

164.  Cross-section  of  canal  for  measurement  of  flow 440 

165.  Current  meters 441 

166.  Grant-Mitchell  meter 442 

167.  Leveler  in  action 443 

168.  Sagebrush  land 446 

169.  The  Boon ' 447 

170.  Shadof  of  Egypt  or  Paecottah  of  India 448 

171.  Caravan  crossing  the  plains  in  early  irrigation  days 455 

172.  Irrigation  canals  are  cut  through  the  mountains 459 

173.  Major  J.  W.  Powell 463 

174.  Completed  diversion  dam  of  the  Truckee  Carson,  Nev.,  pro- 

ject of  the  United  States  Reclamation  Service 465 

175.  Steam  power  digs  the  modern  canals 466 

176.  View  of  the  irrigation  plant  of  the  Utah  Experiment  Station. .  .  467 

177.  Dam  of  Salmon  River  project,  Idaho,  built  by  private  enter- 

prise    468 

178.  Plant  for  the  study  of  the  measurement  and  division  of  water.   469 

179.  Work  for  a  man. .  .  475 


ACKNOWLEDGMENT  FOE 
ILLUSTRATIONS 

The  illustrations  in  this  book  are  either  original  or 
taken  from  the  publications  of  the  United  States  Depart- 
ment of  Agriculture,  the  United  States  Geological  Survey, 
and  the  state  experiment  stations,  with  the  following 
exceptions,  which  have  been  secured  from 
Bark,  Don  H.,  Irrigation  Investigations,  United  States  Department 

of  Agriculture.   Figs.  50,  58,  59,  71,  72,  76,  91,  108,  168,  177. 
Blinn,  P.  K.,  Colorado  Experiment  Station.    Figs.  38,  86,  156. 
Blanchard,  C.  J.,  United  States  Reclamation  Service.    Figs.  6,  49, 

69,  87,  93,  110,  174. 
Bonebright,  J.  E.,  Montana  Experiment  Station.    Figs.  18,  39,  60, 

61,  167. 

Cutler,  Thomas  R.   Fig.  75 
Forbes,  R.  H.   Figs.  22,  66,  83,  90,  117. 
Gillette,  C.  P.,  Colorado  Experiment  Station.    Fig.  178. 
Greeley  Commercial  Club.   Fig.  79. 

Harris,  F.  S.,  Utah  Experiment  Station.   Figs.  16,  19,  26. 
Jardine,  W.  M.,  Kansas  Agricultural  College.   Fig.  73. 
Jarvis,    O.    W.,    Superintendent,    Southern    Nevada    Experiment 

Farm.  Fig.  85. 
Johnson  Company,  The,  Salt  Lake  City.    Figs.  14,  17,  82,  92,  94, 

171,  172,  179. 
McLaughlin,    W.    W.,    Irrigation    Investigations,    United    States 

Department  of  Agriculture.    Figs.  52,  88,  151. 
Ogden  Commercial  Club.   Fig.  81. 
Quinney,  Jos.  E.  Jr.,  Fig.  75. 
Redland's  Commercial  Club.    Fig.  34. . 
San  Jose  Commercial  Club.   Fig.  13. 
Santa  Clara  Commercial  Club.   Fig.  89. 

Smith,  George  Otis,  United  States  Geological  Survey.    Fig.  173. 
Winsor,  Luther  M.,  Utah  Experiment  Station.   Figs.  68,  80,  175. 

Grateful  acknowledgment  is  made  of  the  assistance 
rendered  by  the  above  persons. 

(xxvi) 


THE  PRINCIPLES  OF  IRRIGATION 
PRACTICE 


CHAPTER   I 
THE  MEANING  OF  IRRIGATION 

WATER,  soil,  air  and  sunshine  are  the  four  great  groups 
of  physical  forces  that  determine  the  growth  of  plants.  For 
the  production  of  plant  crops,  all  of  these  must  be  present 
and  active.  Water,  therefore,  is  essential  to  plant-growth 
and  crop-production. 

The  water  that  falls  upon  the  earth  in  the  form  of  rain 
and  snow  is  the  source  of  all  the  water  used  in  agriculture. 
To  be  of  value  in  plant-growth,  this  water  must  be  stored, 
for  longer  or  shorter  periods,  in  the  soil  in  which  plants 
are  growing.  Whenever  the  soil  becomes  too  dry  or  too 
wet,  or  if  the  total  quantity  is  insufficient  or  too  large, 
plant-growth  is  hindered.  It  is  the  concern  of  agriculture 
to  maintain  in  the  soil  the  proper  quantity  of  water  during 
the  growth  of  crops. 

1.  Annual  rainfall. — Water,  in  the  form  of  rain  or 
snow,  falls  over  the  whole  earth.  No  place  is  known  where 
some  rain  does  not  fall  at  some  time  during  the  year. 
However,  the  quantity  that  falls  varies  greatly  in  different 
regions.  Over  the  so-called  deserts  the  annual  rainfall  is 
often  less  than  5  inches,  while  in  various  places  near  the 
seashore  or  among  the  mountains,  the  annual  rainfall 
A  (1) 


2  IRRIGATION  PRACTICE 

exceeds  100  inches  and  occasionally  reaches  600  inches  or 
more,  as  at  Assam,  India.  From  district  to  district,  the 
world  over,  the  quantity  of  water  that  falls  annually 
upon  the  farmers'  fields  is  different. 

2.  Seasonal  rainfall. — Moreover,  the  time  of  the  year 
at  which  the  rain  comes  is  not  everywhere  the  same.    In 
some  localities  the  rain  falls  chiefly  in  summer,  during 
the  season  of  crop-growth;  in  others,  during  the  spring; 
in  others,  during  the  fall,  and  in  yet  others,  during  the 
winter.    Going  eastward  from  the  Pacific  seaboard,  this 
difference  in  seasonal  rainfall  is  well  brought  out.     In 
California,  the  heaviest  rainfall  comes  during  midwinter; 
in  the  Great  Basin,  in  early  spring;  on  the  eastern  slope  of 
the  Rocky  Mountains,  in  late  spring,  and  on  the  Great 
Plains,  near  midsummer.    The  annual  rainfall  may  be 
fairly  large  in  a  given  locality,  but  it  does  not  necessarily 
fall  at  the  time  that  plants  are  growing. 

3.  Variations  in  rainfall. — Added  to  these  variations 
in  the  quantity  of  total  rainfall,  and  in  the  distribution 
throughout  the  year,  is  still  another:   The  same  quantity 
of  rain  does  not  fall  in  the  same  place  from  year  to  year. 
In  one  year  there  may  be  a  large  precipitation,  and  in 
another  a  very  light  one;  and  the  time  of  the  year  of  the 
heaviest  downfall  may  be  shifted  somewhat  from  year 
to  year. 

True,  the  variations  are  not  large.  The  driest  year 
seldom  receives  less  than  two-thirds  the  rainfall  of  the 
wettest  year,  and  usually  it  receives  more.  True,  also,  so 
far  as  our  records  show,  the  average  rainfall  over  a  certain 
locality  for  ten  or  twenty  years  is  practically  constant. 
The  average  rainfall  at  any  one  place  is  nearly  invariable, 
although  distinct  variations  occur  in  successive  years. 
(Fig.  1.) 


MEANING  OF  IRRIGATION 


4.  Conservation  of  rainfall  on  farms. — It  is  the  business 
of  the  farmer  so  to  handle  his  farm  that  the  largest  possible 
proportion  of  the  rain  that  falls  may  be  made  to  enter  the 
soil,  and  to  remain  there  until  needed  by  plants,  unless, 
indeed,  the  rainfall  is  too  heavy,  when  provision  must  be 
made  for  relieving  the  soil  of  the  harmful  surplus.  To 
accomplish  this,  the  farmer  must  resort  to  methods  for 


Ohio  l/af/ey 


I86b-l875  IB 76  -I6»S 


r 


/4 


FIG  1.  Progressive  averages  of  annual  rainfall  (1834-1906). 

preventing,  or  reducing  largely,  the  loss  due  to  the  run- 
off, evaporation  and  seepage.  Where  the  annual  rainfall 
is  fairly  large  and  well  distributed,  these  methods  are 
not  applied  extensively;  but  where  the  annual  rainfall  is 
light  or  is  not  in  the  growing  season,  moisture-conserv- 
ing methods  are  indispensable.  There  are  relatively 
few  localities  on  earth  where  special  efforts  to  conserve 
the  rains  for  plant-growth  are  not  rewarded  by  large 
crop  yields.  The  smaller  the  annual  rainfall,  the  greater 
is,  naturally,  the  return  for  careful  moisture-conservation. 
5.  Conditions  of  dry-farming. — If  the  annual  rainfall 
be  very  light,  it  frequently  happens  that,  with  the  best 
available  tillage  methods,  the  water  conserved  in  the  soil 


4  IRRIGATION  PRACTICE 

is  so  small  that  only  certain  crops  can  be  grown,  and  of 
these  crops  maximum  yields  are  not  obtained.  The  annual 
rainfall,  below  which  special  moisture-conserving  methods 
are  necessary,  is  different  at  different  places.  Ordinarily, 
where  the  rainfall  is  20  inches  or  less,  the  special  water- 
conserving  methods  of  dry-farming  must  be  used.  Where 
the  average  temperature  is  high;  where  heavy  winds 
blow  largely;  where  the  soils  are  shallow  or  infertile,  or 
where  other  water-dissipating  factors  are  especially 
active,  the  methods  of  dry-farming  must  be  employed, 
even  if  the  rainfall  reaches  25  or  30  inches  annually.  On 
the  other  hand,  with  our  present  experience,  we  are 
obliged  to  admit  that  when  the  annual  rainfall  is  less  than 
10  inches,  our  present  methods  of  water-conservation 
are  not  sufficient,  except  in  a  few  special  localities,  to 
make  profitable  crop-production  possible. 

6.  Conditions  of  irrigation. — Wherever  proper  methods 
of  manuring  and  tillage  for  water-conservation  are  insuffi- 
cient to  produce  uniformly  profitable  or  maximum  crops, 
irrigation  is  employed.   The  first  aim  of  the  farmer  should 
always  be  to  store  as  much  as  possible  of  the  natural 
precipitation  in  the  soil,  and  to  apply  water  artificially 
only  to  make  up  the  deficiency  in  the  quantity  of  water 
required  by  plants.    The  quantity  of  irrigation  water, 
then,  needed  on  any  farm,  will  depend  on  the  care  with 
which  the  rainfall  is  conserved  for  the  use  of  plants.   The 
more  thoroughly  water-conservation  methods  are  prac- 
tised, the  smaller  the  quantity  of  irrigation  water  required; 
the  more  carelessly  the  rain-water  is  conserved,  the  larger 
the   quantity   of   irrigation   water   required.     Irrigation 
should  always  be,  and  in  a  good  system  of  agriculture 
always  is,  supplementary  to  the  natural  precipitation. 

7.  Irrigation  defined. — Irrigation  is  the  artificial  appli- 


MEANING  OF  IRRIGATION  5 

cation  of  water  to  lands  for  the  purpose  of  producing  large 
and  steady  crop  yields  whenever  the  rainfall  is  insufficient 
to  meet  the  full  water  requirements  of  crops.  Irrigation  for 
the  purpose  of  disposing  of  sewage  is  of  limited  extent, 
and  is  not  always  true  irrigation. 

8.  Geographical  need  of  irrigation. — The  field  of 
irrigation,  as  above  denned,  is  very  large.  About  25  per 
cent  of  the  earth's  surface  receives  10  inches  or  less  of 
rainfall  annually,  and,  with  our  present  knowledge,  can  be 
reclaimed  only  by  irrigation.  Another  30  per  cent  of  the 


FIG.  2.  The  limited  water  supply  makes  it  unlikely  that  more  than  one-tenth  of 
the  land  will  be  irrigated.    The  shaded  area  is  irrigated. 

earth's  surface  receives  between  10  and  20  inches  of  rain- 
fall annually.  Over  this  vast  area  the  chief  extensive 
crops  may  be  grown  without  irrigation,  but  the  intensive 
crops  demand  the  help  of  irrigation.  That  is,  nearly 
six-tenths  of  the  earth's  surface  will  be  reclaimed,  if  at 
all,  by  irrigation  and  dry-farming.  The  remaining  four- 
tenths  will  be  helped  materially  by  a  system  of  irrigation. 
9.  Possible  extent  of  irrigation. — The  great  rivers 
which,  with  their  numberless  tributaries,  flow  from  the 


6  IRRIGATION  PRACTICE 

highlands  through  the  arid  and  semi-arid  lands,  together 
with  some  of  the  underground  waters,  must  be  the  source 
of  the  water  to  be  used  in  irrigation.  When  a  world-sys- 
tem of  irrigation  shall  be  perfected,  all  of  the  available 
water  will  not,  in  all  probability,  cover  more  than  one- 
tenth  to  one-fifth  of  the  thirsting  land.  The  remainder 
must  be  left  to  be  conquered  by  dry-farming  methods. 
Yet,  the  possible  area  to  be  reclaimed  by  irrigation  is 


FIG.  3.  The  value  of  water  in  an  arid  land.  A  Papago 
squaw,  in  Arizona,  utilizing  the  drip  from  her  water 
bottle  to  grow  a  few  onion  plants  beneath,  protected 
by  a  paling  of  sticks. 

tremendous;  and  in  view  of  its  certainty  of  large  crop 
yield,  farming  under  irrigation  should  be  the  most  attrac- 
tive of  all  modes  of  farming.  (Fig.  2.) 

Irrigation  will  further  find  a  limited  application  in 
humid  countries,  the  occasional  dry  years  of  which  cause 
injurious  droughts.  In  many  of  the  humid  regions  the 


MEANING  OF  IRRIGATION  7 

methods  of  dry-farming  will  often  be  found  to  be  as 
effective  and  less  expensive. 

10.  Mission  of  irrigation  and  dry-fanning. — Irriga- 
tion and  dry-farming  go  hand  in  hand  in  reclaiming  the 
great  countries  under  a  low  rainfall,  and  in  forever  banish- 
ing drought  from  the  earth.  In  this  volume  the  principles 
underlying  a  rational  practice  of  irrigation  are  discussed. 
The  dry-farming  methods  involved  in  irrigation  are  only 
touched  upon  in  passing,  for  they  have  already  been  some- 
what fully  discussed  in  another  volume.* 

REFERENCES 

HENRY.  Weather  Bureau,  United  States  Department  of  Agricul- 
ture, Bulletin  No.  D. 

MEAD,  ELWOOD.  Irrigation  Institutions.  The  Macmillan  Company. 

NEWELL,  F.  H.   Irrigation.   T.  Y.  Crowell  &  Co. 

SMYTHE.  WM.  E.  The  Conquest  of  Arid  America.  The  Macmillan 
Company. 

WIDTSOE,  J.  A.   Dry-Farming.   The  Macmillan  Company  (1910). 

*Widtsoe,  J.  A.,  Dry-Fanning:  A  System  of  Agriculture  for  Countries  under  a 
Low  Rainfall.    The  Macmillan  Company,  New  York. 


CHAPTER  II 
SOIL  MOISTURE 

ALL  bodies  in  the  universe  attract  each  other.  The 
greatest  sun  in  the  heavens  and  the  smallest  speck  of  dust 
under  the  microscope  are  mutually  attracted.  This 
universal  force  of  attraction  finds  different  expressions 
under  varying  conditions.  Thus,  the  heavenly  bodies, 
immense  distances  apart,  are  given  definite  motions  and 
are  held  in  their  places  by  their  mutual  attractions. 
Bodies  near  the  earth  and  belonging  to  it,  instead  of  revolv- 
ing in  space,  fall  to  the  ground  by  virtue  of  this  attrac- 
tion which  the  earth  exercises  upon  all  bodies  on  or  near 
its  surface.  In  both  these  cases  the  attracting  bodies  are 
considerable  distances  apart. 

11.  Attraction  between  near  bodies. — When  the 
attracting  bodies  are  brought  very  near  each  other,  within 
reach  of  the  molecular  forces,  which,  probably  are  only 
expressions  of  the  universal  force,  special  attractions 
are  observed.  For  example,  if  two  plates  of  glass,  evenly 
and  highly  polished,  are  laid  upon  each  other  they,  adhere 
so  firmly  that  it  is  practically  impossible  to  separate 
them.  A  square  of  iron,  with  a  highly  polished  surface, 
may  be  lifted  by  simply  lifting  a  similar  square  which 
has  been  placed  on  the  lower  square  with  the  polished 
surfaces  in  contact.  Two  pieces  of  lead,  with  clean  sur- 
faces, will  adhere  very  firmly,  as  will  also  india-rubber, 
wax  and  similar  substances.  These  attractions  act  only 
through  extremely  small  distances.  If  the  polished  plates 

(8) 


SOIL  MOISTURE  9 

of  glass  are  separated  by  the  thinnest  piece  of  paper, 
they  do  not  adhere;  if  the  iron  surfaces  are  a  trifle  dusty 
they  do  not  adhere.  The  distance  apart  determines 
the  adhesion. 

It  is  generally  held  that  the  ultimate  particles  of  all 
substances  are  held  together  by  molecular  attractions. 
Iron  is  a  solid  mass  and  not  a  pile  of  loose  particles, 
because  of  the  mutual  attraction  of  like  particles,  known  as 
cohesion.  These  molecular  forces  may  be  overcome  by 
other  forces,  notably  by  heat.  When  the  solid  iron  is 
heated,  the  molecular  attraction  is  weakened  until  the 
iron  is  melted.  If  the  heating  is  further  continued,  the 
molecular  attraction  is  finally  overcome,  and  the  iron 
becomes  a  gas,  in  which  state  the  ultimate  particles,  or 
molecules,  actually  repel  each  other. 

This  theory  of  attraction  is  of  great  help  in  under- 
standing the  phenomena  observed  in  soils,  especially  in 
relation  to  water.  When  a  pebble  is  dipped  in  water,  a 
thin  water-film  clings  around  its  whole  extent.  The  water 
has  come  into  very  close  contact  with  the  surface  of  the 
pebble,  within  the  reach  of  molecular  forces,  and  a  cer- 
tain quantity  of  water  adheres.  The  quantity  of  water, 
thus  adhering,  is  just  in  proportion  to  the  force  of  adhesion 
existing  between  the  water  and  the  rock  surface.  On  the 
basis  of  this  fact — the  adhesion  between  rock  surfaces 
and  water — rest  the  tillage  methods  of  moisture-conser- 
vation. 

12.  Soil  particles. — Soil  is  composed  of  broken-down 
rock  mixed  with  decaying  animal  and  plant  remains.  The 
most  notable  properties  of  soil  result  from  the  minute 
size  of  the  constituent  particles.  The  coarsest  particles 
useful  to  plants  are  from  1  to  3  millimeters  in  diameter, 
which  means  that  about  twenty-three  placed  side  by  side 


10 


IRRIGATION  PRACTICE 


would  make  an  inch.  The  finest  are  about  .00001  milli- 
meter in  diameter;  and  it  would  require  about  25,000  of 
them,  placed  side  by  side,  to  make  an  inch.  Most  of  the 
particles  in  an  ordinary  soil  are  of  a  size  intermediate 
between  these  extremes. 

The  smallness  of  the  soil  particles  means  that  the 
number  of  them,  in  an  acre  of  ground  to  a  depth  of  one 
foot,  fairly  transcends  the  human  mind.  If  a  soil  were 
made  up  entirely  of  the  coarsest  particles  above  men- 
tioned, there  would  be,  in  1  cubic  inch,  12,167;  if  of  the 
finest,  there  would  be  in  1  cubic  inch,  15,625,000,000,000 
particles.  These  vast  numbers  of  soil  grains  of  all  sizes 
between  the  extremes  given,  are  jumbled  together  in  the 

soil  in  every  conceiv- 
able manner.  Groups 
and  clusters  of  them 
are  formed;  the  larger 
ones  touch  in  few 
points,  while  the 
smaller  ones  fall  into 
the  spaces  between, 
and  lime  and  other 
substances  often  cause  the  cementing  together  of  parti- 
cles. The  relatively  large  air  spaces  between  the  particles 
and  groups  form  from  30  to  60  per  cent  of  the  whole 
soil  volume.  These  open  or  air  spaces  are  sometimes 
spoken  of  as  pores  or  tubes.  They  are  of  infinite  com- 
plexity of  shape  and  direction  as  they  wriggle  through 
the  soil  mass.  In  spite  of  the  immensity  of  the  numbers 
and  variety  of  the  sizes  of  the  particles,  the  whole 
porous  sytem  is  held  together  as  one,  and  possesses 
definite  properties. 

Of  chief  agricultural  interest  is  the  surface  exposed 


FIG.  4.  Soil  is  a  mixture  of  particles  of  very 
varying  size. 


SOIL  MOISTURE  11 

by  the  soil  particles,  for  it  is  to  these  surfaces  that  the 
soil  water  clings,  and  from  them  that  the  plant-food  is 
largely  derived.  It  is  naturally  very  difficult  to  make 
this  determination  accurately,  but  approximate  figures 
may  be  given.  One  pound  of  the  coarsest  particles  above 
mentioned  would  expose  an  area  of  about  11  square  feet; 
while  one  pound  of  the  finest  particles  would  expose 
about  110,538  square  feet  or  more  than  2%  acres.  The 
surface  of  the  soil  particles  in  1  cubic  foot  of  an  average 
soil,  lying  between  the  two  extremes  described  above, 
would  be  nearly  50,000  square  feet.  The  finer  the  soil, 
the  larger  would  be  the  surface  of  the  soil  particles. 
This  immense  surface  exposed  by  the  particles  of  agri- 
cultural soils  is  of  the  highest  importance  in  agriculture. 

13.  The  soil-moisture  film. — The  result  of  the  attrac- 
tion between  water  and  rocks  is  that  water  added  to  a 
soil  forms  a  film  over  the  surfaces  of  the  particles.  This 
film  is  continuous  so  far  as  the  water  goes,  covering  every 
particle,  bridging  every  point  of  contact  and  filling  every 
minute  opening,  the  diameter  of  which  is  not  greater 
than  the  distance  through  which  the  forces  of  adhesion 
act.  True,  in  every  soil,  even  in  those  composed  of  the 
smallest  particles,  when  the  soil-water  film  is  of  maximum 
thickness,  the  majority  of  the  soil  pores,  which  are  much 
larger  than  the  distance  through  which  adhesion  attrac- 
tion can  act,  are  open  and  free  from  water  except  as  a 
thin  film  may  cling  to  their  sides.  The  shape  of  this  film, 
as  it  fits  accurately  over  every  exposed  surface,  is  a  sym- 
bol of  multiplied  complexity  that  completely  baffles 
human  description  or  understanding. 

When  a  given  quantity  of  water  is  added  to  a  given 
weight  of  soil,  the  thickness  of  the  resulting  soil-mois- 
ture film  depends  entirely  on  the  fineness  of  the  particles 


12  IRRIGATION  PRACTICE 

constituting  the  soil.  This  must  of  necessity  be  so,  for, 
as  has  been  shown,  the  smaller  the  soil  particles  the 
larger  is  the  surface  exposed;  and  the  larger  the  surface, 
the  thinner  will  be  the  film  produced  by  a  given  quantity 
of  water.  The  thickness  of  the  soil-moisture  film  is  of 
considerable  importance,  for  from  it  plants  secure  the 
water  needed  in  their  growth.  If  the  film  be  too  thin, 
that  is,  if  it  is  held  very  firmly,  plants  are  not  able  to  move 
it  from  the  surface  of  the  soil  particle. 

14.  Thickness  of  film  and  diameter  of  particle. — A 
definite  mathematical  relationship  exists  for  any  per 
cent  of  moisture  between  the  thickness  of  the  soil-mois- 
ture film  and  the  diameter  of  the  soil  grains.  If  a  soil  of  a 
specific  gravity  of  2.75  contains  5  per  cent  of  water,  the 
thickness  of  the  soil-moisture  film  is  slightly  more  than 
two  hundredths  of  the  average  diameter  of  the  soil  grains; 
if  10  per  cent,  a  little  more  than  four  hundredths;  if  20 
per  cent,  not  quite  eight  hundredths;  if  30  per  cent,  a 
little  more  than  eleven  hundredths;  and  if  the  soil  con- 
tains 40  per  cent  of  water,  the  thickness  of  the  soil-mois- 
ture film  is  about  fourteen  hundredths  of  the  average 
diameter  of  the  soil  grains. 

That  is,  the  thickness  of  the  soil-moisture  film  in  soils 
that  contain  from  5  to  40  per  cent  of  moisture,  varies 
from  two  hundredths  to  fourteen  hundredths  of  the 
diameter  of  the  average  soil  grains.  When  the  very  small 
sizes  of  the  particles  themselves  are  considered,  this 
shows  the  extreme  thinness  of  the  soil-moisture  films, 
with  which  agriculture  has  to  deal.  Meanwhile,  it  must 
be  remembered  that  only  very  fine  soils  can  hold  as  much 
as  40  per  cent  of  water.  When  the  thickness  of  the  soil- 
moisture  film  is  somewhere  in  the  neighborhood  of  one 
fifty-thousandth  of  an  inch,  it  is  probably  near  its  maxi- 


SOIL  MOISTURE  13 

mum  thickness,  and,  when  this  has  been  reached,  there  are 
in  average  soils  about  20  per  cent  of  moisture. 

15.  Hygroscopic  coefficient. — If  a  thoroughly  dried 
soil  be  exposed  to  air,  which  is  always  somewhat  moist, 
the  attraction  between  the  soil  surface  and  the  water 
vapor  in  the  air  immediately  becomes  active.  Some  of 
the  water  vapor  condenses  upon  the  surfaces  of  the  soil 
grains  to  form  the  beginnings  of  the  film.  This  coating 
of  water  is  hygroscopic  soil  moisture.  If  the  air  sur- 
rounding the  soil  is  saturated  with  water  vapor,  the 
largest  possible  quantity  is  condensed  upon  the  soil. 
The  percentage  of  moisture  representing  the  full  con- 
densation of  water  upon  soil  from  such  saturated  air, 
under  given  conditions  of  temperature,  is  known  as  the 
hygroscopic  coefficient. 

The  water  thus  taken  from  the  air  is  not  wholly  held 
as  surface  film.  In  every  soil  are  certain  substances 
(colloidal)  that  absorb  water  to  form  loose  chemical  com- 
binations. Such  materials  are  well  represented  by  the 
jellies  which  hold  large  quantities  of  water  uniformly 
distributed  throughout  their  mass.  Among  the  substances 
with  more  or  less  strongly  marked  jelly-like  properties 
are  clay,  hydrate  of  iron,  humus  and  decaying  organic 
matter  generally,  and  a  number  of  gums,  among  which 
gum  tragacanth  is  the  most  notable. 

The  hygroscopic  coefficient,  therefore,  increases  as 
the  fineness  of  the  soil  increases,  and  as  the  quantity  of 
the  water-absorbing  substances  increases.  For  example, 
Lyon  and  Fippin  found  that  very  fine  sand  absorbed  1.8 
per  cent  of  hygroscopic  moisture;  silt,  7.3  per  cent;  clay, 
16.5  per  cent,  and  a  muck  soil  absorbed  48  per  cent  of 
water  from  saturated  air.  Hilgard  examined  three  soils 
very  much  alike,  except  that  one  contained  4  per  cent, 


14  IRRIGATION  PRACTICE 

the  other  19.83  per  cent,  and  the  third  51  per  cent  of  iron 
hydrate.  The  hygroscopic  coefficient  of  the  first  was 
4.92  per  cent;  of  the  second,  15.40  per  cent,  and  of  the 
third,  19.66  per  cent.  At  the  Utah  Station  it  was  found 
that  on  the  dry-farms,  in  the  fall,  after  the  baking  heat 
of  summer  and  before  the  autumn  rains,  the  soil  moisture 
remaining  was  in  proportion  to  the  clay  contained  by 
the  soils. 

The  hygroscopic  moisture  is  held  very  firmly  by  the 
soil,  and  it  is  very  doubtful  if  it  has  any  direct  value  for 
plants.  The  part  clinging  around  the  soil  grains  probably 
has  no  such  value,  but  it  is  possible  that  the  colloidal 
soil  constituents  often  containing  much  water  may  be 
made  to  give  up  some  of  their  water  to  the  growing  plant. 
King  has  suggested  that  in  seasons  of  drought  the  hygro- 
scopic water  may  evaporate  at  one  point  in  the  soil  and  be 
condensed  elsewhere  upon  the  root-hairs  in  search  of  water. 
The  chief  agricultural  interest  of  hygroscopic  soil  mois- 
ture is  that  upon  it  and  possibly  in  part  by  it,  is  held  the 
water  which  really  can  be  used  by  plants. 

16.  The  wilting  coefficent. — Water  added  to  a  soil, 
the  hygroscopic  coefficient  of  which  has  been  satisfied, 
simply  thickens  the  soil-moisture  film  or  more  com- 
pletely saturates  the  colloidal  soil  constituents.  The 
first  water  thus  added  above  hygroscopic  saturation  is 
also  held  very  firmly  and  is  of  little  or  no  direct  value  to 
plants.  As  more  water  is  added,  however,  and  the  film 
is  thickened  around  the  soil  grains,  the  outer  layers  of  the 
film  water  are  held  with  less  and  less  force,  and  a  point 
is  at  last  reached  above  which  plants  can  use  the  soil 
moisture  in  growth,  although  it  may  be  with  some  diffi- 
culty. Whenever  the  soil  moisture  in  a  cropped  field  is 
reduced  to  this  point,  the  plants  growing  on  the  soil 


SOIL  MOISTURE  15 

begin  to  wilt,  and  growth  practically  ceases.  The  per- 
centage of  moisture  corresponding  to  this  point  is  called 
the  uniting  coefficient. 

According  to  the  researches  of  Briggs  and  Shantz, 
the  wilting  coefficient  is  about  one  and  one-half  times  the 
hygroscopic  coefficient.  That  is,  in  a  soil  with  a  hygro- 
scopic coefficient  of  6  per  cent  of  water,  the  wilting  coeffi- 
cient would  be  about  9  per  cent.  This  relative  value  of 
the  wilting  coefficient  appears  to  be  confirmed  by  field 
experiments  conducted  at  the  California  and  Utah 
Experiment  Stations. 

The  wilting  coefficient,  like  the  hygroscopic  coefficient, 
varies  with  the  soil  used.  In  sandy  soils  it  is  low,  often 
less  than  1  per  cent  of  moisture;  in  clay  soils  higher, 
often  more  than  16  per  cent,  and  in  extremely  heavy  clays 
as  high  as  30  per  cent;  in  the  average  loam,  about  10  per 
cent  of  moisture.  It  is  ordinarily  thought  that  plants 
differ  markedly  in  their  power  of  reducing  the  soil  mois- 
ture before  wilting.  Recent  researches  do  not  bear  out 
this  view.  On  a  given  soil,  under  like  meteorogical  con- 
ditions, the  wilting  coefficient  is  within  1  to  3  per  cent 
of  each  other  for  all  the  ordinary  plants  at  the  same 
period  of  growth,  whether  grown  under  arid  or  humid 
conditions. 

While  growth  undoubtedly  ceases  at  wilting,  yet  the 
plant  may  slowly  take  up  some  of  the  moisture  held 
in  the  soil  below  the  wilting  point.  On  the  other  hand, 
under  proper  methods  of  agriculture  the  soil  moisture  is 
seldom  reduced  to  the  wilting  point,  especially  on  deep 
soils,  if  irrigation  has  been  practised  regularly.  At  the 
Utah  Station,  several  crops,  in  their  medium  stages  of 
growth,  were  allowed  to  go  for  long  periods,  from  twenty- 
seven  to  fifty-five  days,  without  irrigation.  At  the  close 


16 


IRRIGATION  PRACTICE 


of  the  periods,  the  grain  crops  and  the  peas  were  prac- 
tically ripened.  No  noticeable  injury  from  wilting  was 
observed.  Some  of  the  results  are  presented  in  the  fol- 
lowing table: 


Crop 

Days 
after 
irrigation 

Per  cent 
of  water  in 
first  foot 

Average  per 
cent  of  water 
to  a  depth  of 
6  to  8  feet 

Wheat 

38 

626 

8  21 

Oats 

32 

7  57 

9  98 

Corn 

47 

9.28 

10  03 

Peas  .        .        .    . 

27 

7.66 

10.68 

Lucern      .... 

31 

8.34 

Potatoes   ....            .    . 

31 

9.07 

11.62 

The  hygroscopic  coefficient  of  the  soil  was  about  5 
per  cent,  which  would  make  the  wilting  coefficient  about 
7J/2  per  cent.  In  only  one  case,  that  of  wheat,  did  the 
soil  moisture  go  below  this  point  in  the  first  foot;  and,  in 
every  case,  the  percentage  of  soil  moisture  to  a  depth  of 
6  to  8  feet,  through  all  of  which  root-action  was  felt,  was 
above  the  calculated  wilting  coefficient. 

17.  Lento-capillary  point. — The  water  in  the  soil- 
moisture  film  corresponding  to  the  wilting  coefficient  is 
held  so  firmly  that  plants  can  absorb  it  with  difficulty. 
As  more  water  is  added  to  the  soil,  to  thicken  the  film, 
the  more  loosely  is  the  water  held,  and  consequently  the 
more  easily  can  plants  secure  it.  As  this  thickening 
goes  on,  a  point  is  reached  above  which  the  film  water  is 
held  so  loosely  that  it  moves  freely  from  soil  particle  to 
soil  particle  under  the  influence  of  the  forces  in  the  soil. 
This  has  been  called  the  lento-capillary  point.  The  water 
above  this  point  is  readily  available  to  plants,  and  con- 
stitutes the  main  supply  of  water  for  plants  under  irri- 
gated conditions. 


SOIL  MOISTURE  17 

Whenever  the  soil  moisture  is  above  the  lento-capil- 
lary point,  plants  secure  their  water  with  the  least  expendi- 
ture of  energy,  and  it  should  therefore  be  the  purpose 
of  irrigation  to  maintain  the  moisture  in  the  soil  above 
this  point,  at  least  during  the  periods  of  most  rapid  plant- 
growth.  In  practice,  this  is  usually  done,  except  in  sea- 
sons of  water-shortage.  The  practical  irrigator  recog- 
nizes the  need  of  irrigation  by  a  faint  change  in  the  color 
and  rigidity  of  the  plants — possibly  a  condition  prelim- 
inary to  wilting.  When  this  occurs,  the  soil  moisture  is 
ordinarily  just  above  or  below  the  lento-capillary  point. 

During  two  summers,  on  the  experimental  fields  of 
the  Utah  Experiment  Station,  the  moisture  in  the  soil 
was  determined  immediately  before  each  of  several  hun- 
dred irrigations.  In  the  first  year,  the  percentage  of  soil 
moisture  was  13.17;  in  the  second,  13.  In  every  case, 
the  practical  irrigator  declared  the  field  in  need  of  irriga- 
tion. The  lento-capillary  point  was  determined  for  this 
soil  to  be  about  12.68  per  cent,  or  almost  identical  with 
the  percentage  of  soil  moisture  at  which  irrigation  was 
declared  advisable. 

18.  Maximum  capillary  capacity. — As  the  'soil-mois- 
ture film  is  thickened  by  the  further  additions  of  water 
above  the  lento-capillary  point,  the  force  with  which  the 
outer  layers  of  water  is  held  becomes  weaker  and  weaker. 
At  last  a  point  is  reached  above  which  no  more  water 
can  be  taken  up.    When  this  thickness  of  the  film  is 
reached,  new  additions  of  water  simply  slide  off  the  film 
and  are  drawn  away  by  gravity.    This  is  the  point  of 
maximum  capillary  capacity. 

19.  Free  water. — Water  added  to  a  soil  above  the 
maximum    capillary    capacity    is    called    free   water.     It 
moves  slowly  downward  through  the  pores  and  tubes  of 

B 


18  IRRIGATION  PRACTICE 

the  soil  until  it  is  all  absorbed  by  the  lower  drier  soil  or 
until  it  communicates  with  the  standing  water-table. 

Soil  moisture  is  the  term  used  to  designate  the  water 
held  in  the  capillary  condition  in  soils.   Soil  water  denotes 


FIG.  5.  The  moisture  film  surrounding  a  soil  particle.  The  black  part  represents 
a  segment  of  the  particle,  (b)  Hygroscopic  coefficient;  (c)  wilting  coeffi- 
cient; (d)  lento-capillary  point;  (e)  point  of  maximum  capillarity;  (d-e) 
freely  moving  capillary  moisture. 

the  free  water,  that  beyond  capillary  saturation,  which 
may  exist  in  soils.  Many  books  on  agriculture  speak  of 
the  maximum  water  capacity  of  soils,  meaning  the  water 
held  in  a  volume  of  soil  artificially  confined  in  a  funnel  or 


SOIL  MOISTURE  19 

tube,  when  the  air  spaces  in  the  soil  are  completely  filled 
with  water.  This  constant  has  no  great  agricultural  value. 
It  represents  a  condition  that  should  be  avoided  so  far 
as  is  possible  in  farming  under  irrigation,  except  in  the 
top  foot  of  the  soil  while  water  is  actually  being  applied 
to  the  land. 

20.  Summary. — The  principles  upon  which  rational 
irrigation  practices  are  built,  rest  upon  the  facts  pre- 
sented in  this  chapter.  The  attraction  existing  between 
soils  and  water  causes  water  to  cling  as  a  film  around  the 
soil  grains.  The  hygroscopic  coefficient  represents  the 
water  which  is  condensed  from  the  water  vapor  of  sat- 
urated air;  it  is  of  no  practical  value  to  plants.  The  wilt- 
ing coefficient,  about  one  and  one-half  times  the  hygro- 
scopic coefficient,  represents  the  point  below  which  plants 
can  not  secure  sufficient  water  from  the  soil  for  their  needs. 
The  lento-capillary  point  is  the  point  above  which  the 
soil  moisture  is  readily  available  to  plants.  Above  this 
point,  also,  film  water  moves  freely  in  obedience  to  the 
laws  of  capillarity.  The  maximum  capillary  capacity 
represents  the  point  at  which  the  attraction  between 
the  soil  surface  and  water  ceases  to  be  active;  it  is  satu- 
rated. From  the  first  hygroscopic  coating  to  the  maximum 
capillary  water  capacity,  the  water  is  said  to  be  in  a  capil- 
lary state.  Any  water  added  above  this  point  is  free 
water  moving  in  obedience  to  the  pull  of  gravity.  (Fig.  5.) 

Much  excellent  work  has  been  done  on  soil  moisture 
by  investigators,  both  in  Europe  and  America.  F.  H. 
King,  E.  W.  Hilgard,  Milton  Whitney  and  his  associates, 
have  done  much  of  the  American  work.  Unfortunately, 
for  the  arid  regions,  most  of  the  work  on  soil  moisture 
has  been  done  under  humid  conditions.  For  instance, 
capillarity  has  been  studied  almost  entirely  by  placing 


20  IRRIGATION  PRACTICE 

tubes  filled  with  soil  in  pans  containing  water,  and  the 
upward  movement  has  been  studied.  This  is  of  little 
interest  to  the  arid  regions.  Much  profitable  work  may 
be  done  for  irrigation  by  the  careful  study  of  the  move- 
ment of  water  applied  to  soils  as  under  irrigated 
conditions. 

REFERENCES 

BRIGGS,  LYMAN  J.  The  Mechanics  of  Soil  Moisture.   United  States 

Department  of  Agriculture,  Bulletin  No.  10  (1897). 
BRIGGS,  LYMAN  J.,  and  SHANTZ,  H.  L.   The  Wilting  Coefficient  for 

Different    Plants,    and    Its    Indirect   Determination.     United 

States  Department  of  Agriculture,  Bureau  of  Plant  Industry, 

Bulletin  No.  230  (1912). 

HILGARD,  E.  W.   Soils.   Chapters  VI  and  XIII  (1906). 
KING,  F.  H.   Physics  of  Agriculture.   Chapters  IV  and  V  (1901). 
WIDTSOE,  J.  A.,  and  MCLAUGHLIN,  W.   W.    The   Movement   of 

Water  in  Irrigated  Soils.   Utah  Experiment  Station,  Bulletin 

No,  115  (1912). 


CHAPTER  III 

THE  SOIL  AS  WATER  RESERVOIR 

IN  an  ideal  system  of  irrigation,  water  would  be 
applied  continuously  to  the  soil,  and  at  a  vrate  to  meet 
the  actual  requirements  of  the  plants  growing  on  it. 
Except  in  a  very  few  cases,  this  ideal  method  is  impossi- 
ble. In  practice,  lands  are  watered  intermittently. 
When  the  "turn  to  water"  comes,  the  farmer  applies  to 
the  soil  in  a  few  hours,  or  in  a  few  days  at  most,  as  much 
water  as  he  is  allowed,  or  as  he  believes  will  supply  the 
crop  until  the  next  turn  comes,  which  may  be  a  few  days 
or  several  weeks  hence.  Even  in  cases  where  the  farmer 
has  at  his  disposal  a  continuous  flow  of  water,  it  is  sel- 
dom practicable  or  wise  to  attempt  continuous  irrigation 
of  any  one  field.  Irrigation  is  essentially  an  intermit- 
tent practice. 

Plants  can  not  live  long  without  water.  When  the 
water  in  the  soil  is  reduced  to  the  definite  limit  known  as 
the  wilting  coefficient,  plants  may  be  seriously  injured  in 
a  few  hours,  unless  more  water  is  added  to  the  soil.  In 
view  of  this  fact  and  the  common  knowledge  that  crops 
thrive  under  systems  of  irrigation-rotation,  it  is  evi- 
dent that  water  applied  in  irrigation  is  held  by  the  soil 
in  quantities  sufficient  to  maintain  crops  in  a  good  con- 
dition until  the  next  watering  occurs.  That  is,  water 
may  be  stored  in  the  soil  in  considerable  quantities.  The 
property  of  soils  to  act  as  storage  reservoirs  for  water  is 
of  the  highest  importance  in  the  practice  of  irrigation. 

(21) 


22  IRRIGATION  PRACTICE 

21.  Irrigated  soils  are  unsaturated. — In  all  proper 
irrigation  practice,  the  farmer  is  dealing  with  unsaturated 
soils.  Many  of  the  best  results  of  irrigation  are  due  to 
this  condition;  and  the  irrigation  practices  to  be  out- 
lined refer  largely  to  soils  which  are  not  fully  saturated 
with  water. 

Water  should  ordinarily  be  applied  to  crops  when  the 
water  in  the  soil  has  reached  the  point  of  lento-capillarity 
as  described  in  the  preceding  chapter;  that  is,  the  point 
below  which  capillary  movements  become  very  slow. 
When  the  soil  water  has  been  exhausted  to  this  point, 
the  plant  is  obliged  to  expend  an  unnecessary  amount  of 
energy  in  securing  water,  and  the  soil  should  be  irrigated. 
Experienced,  practical  irrigators  declare  that  irrigation 
is  necessary  about  the  time  this  point  has  been  reached. 
It  may  usually  be  recognized  by  a  flabbiness  and  a  slight 
change  of  color  in  the  leaves  and  stalks  of  the  plants. 

The  percentage  of  moisture  in  the  soil  which  corres- 
ponds to  this  point  of  slow  capillary  motion  varies  accord- 
ing to  the  fineness  of  the  soil.  In  coarse  soils  it  may  be 
below  10  per  cent;  in  fine  clayey  soils,  20  per  cent  or 
more.  For  average  loam  soils  it  is  in  the  neighborhood 
of  12  or  13  per  cent. 

The  maximum  capacity  for  capillary  soil  moisture 
also  varies  with  the  soil.  In  coarse  sandy  soils  it  fre- 
quently falls  to  12,  or  even  10,  per  cent;  in  fine  clayey 
soils  it  rises  to  30  or  40,  or  more,  per  cent.  In  average 
loam  soils  it  is  not  far  from  24  per  cent. 

The  water  actually  used  in  a  wise  system  of  irrigation 
varies,  then,  between  the  maximum  capillary  saturation 
and  the  point  of  lento-capillarity,  which,  in  an  ordinary 
loam  soil,  is  a  variation  of  from  24  to  12  per  cent.  This 
must  be  supplied  from  time  to  time  by  irrigation;  but, 


SOIL  AS  WATER  RESERVOIR  23 

the  usual  quantities  of  water  added  in  irrigation  seldom, 
if  ever,  are  sufficient  to  bring  the  soil  beyond  the  first  or 
second  foot  to  maximum  capillary  saturation. 

The  quantity  of  water  that  may  be  applied  in  any  one 
irrigation  depends  somewhat  upon  the  nature  of  the  soil, 
yet  varies  within  rather  narrow  limits.  It  is  seldom  pos- 
sible to  apply  at  one  irrigation  less  than  2  inches,  and 
practically  impossible  to  apply  more  than  10  inches, 
unless  the  soil  be  very  gravelly.  The  practical  limits  are 
yet  narrower;  a  light  irrigation  is  about  3  inches,  a  heavy 
one  about  8  inches;  and  an  average  one  from  5  to  6  inches. 

One  inch  of  water  is  equivalent  to  3  per  cent  of  soil 
moisture  to  a  depth  of  one  foot.  A  heavy  irrigation  of 
8  inches  would,  therefore,  raise  the  soil  moisture  in  1 
foot  of  thoroughly  dry  loam  soil  to  24  per  cent,  or  maxi- 
mum capillary  saturation.  If  the  soil,  at  the  time  of 
irrigation,  contains  12  per  cent  of  moisture,  one  such 
heavy  irrigation  would  raise  2  feet  of  soil  to  full  capillary 
saturation.  Since  the  moisture  in  the  upper  8  to  10  feet 
is  concerned  in  plant-production,  the  full  soil  column 
under  such  irrigation  is  far  from  saturation.  In  fact,  a 
loam  soil,  containing  12  per  cent  of  moisture,  will  con- 
tain, after  receiving  a  heavy  irrigation  of  8  inches,  not 
more  than  an  average  of  15  per  cent  to  a  depth  of  8  feet; 
while  the  full  saturation  is  about  24  per  cent.  With  a 
medium  irrigation  of  about  5  inches  the  unsaturated 
character  of  the  soil  would  be  still  more  marked. 

22.  The  movement  of  soil  moisture. — The  water 
added  to  soils  by  irrigation,  instead  of  saturating  the 
upper  soil  a  foot  or  two,  distributes  itself  with  great 
regularity  to  considerable  depths  in  the  soil.  All  soil 
moisture  is  acted  upon  by  the  two  chief  contending 
forces  of  gravitation  and  adhesion.  Gravity  tends  to 


I 


SOIL  AS  WATER  RESERVOIR  25 

pull  the  moisture  downward,  while  the  attraction  between 
the  soil  and  the  water  tends  to  hold  it  as  a  film  around  the 
soil  grains.  The  actual  movement  of  a  particle  of  water 
in  a  soil  is  a  resultant  of  these  forces. 

In  general,  water  moves  from  the  thicker  to  the 
thinner  soil  film.  Immediately  after  an  irrigation,  when 
the  upper  soil  layers  are  wettest,  the  water  moves  down- 
ward; immediately  before  an  irrigation,  when  the  plants 
have  largely  exhausted  the  upper  soil  layers  of  water, 
the  soil  water  is  moving  slowly  upward.  The  down- 
ward movement,  aided  by  gravity,  is  more  rapid  than 
the  upward  movement  against  gravity.  The  film  of  soil 
moisture  is  usually  in  a  state  of  motion,  attempting  to 
place  itself  in  equilibrium  with  the  many  contending 
forces  in  the  soil.  As  examples,  the  moisture  in  the  soil 
moves  in  all  directions  toward  a  point  at  which  a  root- 
hair  is  absorbing  water;  and,  as  evaporation  occurs  at 
the  soil  surface,  there  is  a  general  upward  movement  of 
the  soil  moisture  to  supply  the  loss. 

The  drier  the  soil,  the  slower  does  the  soil  moisture 
move.  Under  the  point  of  lento-capillarity,  soil-mois- 
ture movements  occur  with  great  difficulty;  above  this 
point,  they  occur  with  great  freedom.  One  proof  of  this 
is  that  at  depths  of  8  to  10  feet,  where  plant  roots  pene- 
trate in  small  numbers  only,  the  moisture  is  seldom 
reduced  below  the  lento-capillary  point,  while  nearer 
the  surface  and  abundant  root-action  the  moisture  is 
often  reduced  to  the  wilting  coefficient. 

23.  The  distribution  of  soil  moisture. — After  a  sur- 
face irrigation  of  a  soil  with  a  water  content  near  the 
lento-capillary  point,  the  upper  soil  layers  are  invariably 
wetter  than  the  lower  ones.  Any  deviation  from  this  rule 
is  only  apparent  and  is  due  to  the  fact  that  the  subsoil 


26 


IRRIGATION  PRACTICE 


contains  more  clay  or  other  fine  particles  than  the  top 
soil,  and  therefore  has  a  higher  water-holding  power  per 
unit  weight  of  soil.  When  the  thickness  of  the  soil-mois- 
ture film  is  considered,  there  is,  immediately  after  an 
irrigation,  a  steady  diminution  with  increasing  depth. 
In  soils  of  approximately  uniform  structure,  this  is  well 
brought  out,  as  in  the  following  table,  taken  from  the 
work  of  the  Utah  Station.  In  this  table  are  shown  the 
percentages  of  water  in  each  foot  to  a  depth  of  8  feet, 
one  or  two  days  after  irrigations  of  various  depths,  and 
in  early  spring  after  the  winter  precipitation  has  dis- 
tributed itself. 


Depth  of  water  applied 

In  the 
spring 

7.5 
inches 

5  inches 

2.5 
inches 

1st  foot 

23.80 
21.88 
20.17 
17.72 
15.91 
14.55 
14.21 
14.15 

23.56 
20.73 
19.09 
17.84 
16.29 
15.83 
15.60 
14.81 

18.57 
13.81 
13.53 
13.46 
12.32 
11.81 
12.31 
12.70 

18.42 
17.49 
15.65 
14.07 
13.98 
13.14 
13.26 
12.93 

2d  foot 

3d  foot 

4th  foot     .    .             .    . 

5th  foot  -.    . 

6th  foot  

7th  foot  

8th  foot 

This  distribution  of  soil  moisture  may  be  explained 
as  follows:  Water  added  to  a  soil  first  saturates  the  upper 
soil  layers  thoroughly,  and  there  is  a  tendency  to  keep 
the  top  soil  as  near  as  possible  to  this  point  of  maximum 
capillary  saturation.  Then,  the  lower  drier  layers  begin 
to  draw  water  downward.  The  wettest  particles  are  near 
the  top;  the  lower  particles  are  all  attracting  the  water. 
As  water  moves  downward  through  the  thin  capillary 
film,  friction  has  to  be  overcome.  The  farther  the  parti- 
cle is  away  the  more  friction  must  be  overcome.  The 
water  above  the  point  of  lento-capillarity  therefore 


SOIL  AS  WATER  RESERVOIR 


27 


tends  to  distribute  itself  inversely  with  the  distance  of  a 
soil  particle  from  the  wettest  particle  which  is  the  source 
of  supply;  that  is,  after  an  irrigation,  the  soil-moisture 
film  will  be  thickest  in  the  top  foot,  and  will  become 
steadily  thinner  in  the  lower  soil  layers.  (Fig.  7.) 

If  the  soil  is  very  dry,  say  near  the  wilting  coefficient, 
when  an  irrigation  occurs,  the  downward  movement 
of  water  is  slow.  Under  such  a  condition  the  upper  soil 
sections  remain  saturated  until  the  moisture  in  the  lower 


Percenr  of  water   /rt  30 /'/ 


FIQ.  7.  Distribution  of  water  in  soil  immediately  after  an  irrigation. 


28  IRRIGATION  PRACTICE 

layers  has  gone  above  the  point  of  slow  capillarity. 
Whenever  that  has  been  done,  the  moisture  moves  down- 
ward freely  in  obedience  to  the  law  already  stated.  This 
is  really  a  matter  of  common  experience,  in  opening  any 
irrigation  project  in  the  arid  region.  The  farmer  finds 
that  the  water  does  not  penetrate  the  soil  deeply  the 
first  year  of  irrigation;  but,  as  time  goes  on,  the  soil 
becomes  wetter  to  greater  depths,  and  at  the  same  time 
less  water  is  required  to  produce  crops.  The  moisture 
content  of  the  native  undisturbed  soil  in  arid  regions  is 
usually  below  the  point  of  lento-capillarity.  The  first 
water  added  is  used  to  bring  the  moisture  content  up  to 
this  point.  As  this  is  accomplished,  water  moves  downward 
freely;  and  plants,  also,  are  enabled  to  secure  their  water 
supply  with  a  smaller  expenditure  of  energy. 

The  above  law  of  distribution,  which  appears  to  hold 
for  all  unsaturated  soils,  above  lento-capillarity,  is  a 
provision  of  nature  of  utmost  importance  in  the  economic 
use  of  irrigation  water.  Though  water  moves  steadily 
downward  after  an  irrigation,  by  far  the  largest  propor- 
tion is  held  near  the  surface  where  plants  can  use  it.  It 
has  been  roughly  estimated,  on  the  basis  of  the  law  of 
distribution,  that  on  a  deep  soil  with  a  moisture  per- 
centage at  the  point  of  lento-capillarity,  85  per  cent  of 
a  heavy  irrigation  will  be  held  in  the  upper  10  feet,  within 
reach  of  plants.  By  reducing  the  irrigations  properly,  it 
is  possible  to  prevent  practically  any  of  the  irrigation 
water  from  descending  below  the  zone  of  plant  activity. 
On  the  other  hand,  if  water  is  applied  to  a  soil  too  fre- 
quently or  in  excessive  quantities,  the  excess  will  slide 
downward  to  great  depths,  to  reappear  somewhere  as 
seepage  or  drainage  water.  A  good  understanding  of  this 
principle,  properly  applied  in  irrigated  districts,  will  do 


SOIL  AS  WATER  RESERVOIR  29 

much  to  lessen  the  danger  of  injury  from  water-logged 
and  alkali  lands. 

In  ordinary  practice,  lands  should  not  be  irrigated 
until  the  crop  has  reduced  the  soil-moisture  content 
nearly  to  the  lento-capillary  point,  and  a  little  lower  in 
the  upper  layers.  Then  only  enough  water  should  be 
applied  to  supply  the  zone  of  crop-action,  say  10  or  12 
feet.  This  quantity  varies,  in  different  soils,  but  seldom 
exceeds  a  depth  of  6  inches  at  an  irrigation. 

24.  Field  moisture  capacity. — The  law  of  distribu- 
tion of  water  in  soils  makes  it  clear  that  the  average 
percentage  of  water  held  in  a  soil  to  a  depth  of  say  10  feet, 
after  even  a  heavy  irrigation,  is  far  below  the  maximum 
capillary  water  capacity.  Under  the  conditions  prevail- 
ing in  irrigated  districts,  except  when  over-irrigation  is 
practised,  the  top  foot  or  often  the  top  layer  contains 
only  the  maximum  capillary  percentage  of  moisture. 
The  percentage  becomes  steadily  smaller  with  increasing 
depth  until,  at  8  to  15  feet,  it  is  very  little  above  the 
point  of  slow  capillary  motion.  This  is  especially  well 
brought  out  in  the  spring,  in  districts  where  the  precipita- 
tion conies  chiefly  in  the  winter  time.  In  early  spring, 
after  the  water  from  the  winter  snows  and  rains  has 
soaked  into  the  soil  and  distributed  itself,  it  was 
found  that,  in  the  Utah  experiments,  a  soil  with  a  maxi- 
mum capillary  capacity  of  25  per  cent  invariably  con- 
tained, to  a  depth  of  8  feet,  an  average  of  18  or  19  per 
cent  of  moisture.  Crawley  observed  similarly  that  certain 
Hawaiian  soils  of  a  maximum  capillary  capacity  of  32  to 
39  per  cent  contained  in  the  field  only  22  to  29  per  cent 
of  moisture.  The  percentage  of  moisture  held  in  field 
soils  to  a  depth  of  8  to  10  feet,  when  the  top  foot  is 
saturated,  may  be  called  the  field  water  capacity  of  a 


30  IRRIGATION  PRACTICE 

soil.  It  is  not  far  from  the  optimum  water  content  for 
plant-growth. 

25.  Water  distribution  in  furrow  irrigation. — Wher- 
ever the  water  supply  is  plentiful,  irrigation  by  some 
form  of  the  flooding  method  is  largely  employed.  Where 
water  is  scarce  and  smaller  quantities  must  cover  equal 
areas  of  land,  the  furrow  method  of  irrigation  is  almost 
invariably  practised.  With  certain  crops,  and  on  certain 
lands,  even  if  the  water  supply  is  large,  the  furrow 
method  of  irrigation  is  preferred. 

Water  applied  in  a  furrow  moves  not  only  vertically 
downward,  but  in  every  direction  from  the  wetted  fur- 
row. The  movement  downward,  aided  by  the  full  force 
of  gravity,  is  the  most  rapid;  it  diminishes  as  it  becomes 
more  horizontal.  That  is,  the  lateral  is  smaller  than  the 
downward  movement.  It  is  a  common  experience  that 
the  lateral  capillary  movement  of  water  near  the  surface 
of  deep  soils,  is  slight.  In  an  average  loam  soil  it  is  sel- 
dom more  than  6  feet  from  the  wetted  center;  in  clay 
soils  larger;  in  sand  soils  smaller.  The  law  of  distribution 
is  of  the  same  nature  as  for  the  downward  movement. 

If  neighboring  furrows  are  not  too  far  apart,  the 
moisture  films  moving  in  all  directions  from  them  finally 
meet,  until,  at  certain  depths,  depending  on  the  nature 
of  the  soil  the  size  and  distance  apart  of  the  furrows,  and 
the  quantity  of  water  used,  the  percentage  of  water  is 
practically  the  same,  whether  under  or  between  the  fur- 
rows. Loughridge,  in  a  study  of  California  orchards, 
when  the  furrows  were  from  6  to  8  feet  apart,  showed  this 
to  be  true  for  a  variety  of  soils.  In  the  Utah  work,  on  a 
loam  soil,  at  depths  of  5  and  6  feet,  there  was  little  dif- 
ference in  the  moisture  content  under  furrow  or  row, 
when  the  furrows  were  about  3  feet  apart.  The  longer 


Clay  Loam. 
1ft.       0          1ft. 


Sandy  Soil. 
2ft.     1ft.      0          m.      2/t. 


72  HOURS  AFTER  IRRIGATION 
FIG.  8.  Distribution  of  water  in  soil  under  furrow  irrigation. 


(31) 


\ 


32  IRRIGATION  PRACTICE 

the  water  flows,  the  more  completely  will  the  lower  soil 
layers  be  provided  with  the  same  percentage  of  water. 
In  all  cases,  the  law  of  distribution  will  be  the  same, 
except  as  modified  by  the  full  or  partial  help  given  by 
gravity,  according  to  the  direction  in  which  the  move- 
ment is  taking  place.  (Fig.  8.) 

26.  Effect  of  hardpan. — A  layer  through  which  water 
can  pass  with  great  difficulty,  if  at  all,  is  often  found  a 
short  distance  below  the  soil  surface.  Sometimes  it  is 
merely  the  "plowsole,"  resulting  from  the  repeated  plow- 
ings  of  a  somewhat  clayey  soil  to  the  same  depth.  More 
often  it  results  from  the  mutual  relations  of  climate  and 
soil.  For  example,  in  a  country  where  the  rainfall  is 
heavy,  the  very  fine  particles  of  a  heavy  clay  soil  are 
washed  downward,  until  the  whole  subsoil  becomes  more 
or  less  impervious  to  water.  In  regions  of  light  rainfall, 
that  is,  in  true  dry-farming  and  irrigation  regions,  this 
washing  down  of  fine  material  stops  abruptly  at  a  point 
representing  the  depth  of  penetration  of  the  rainfall. 
Approximately  the  same  quantity  of  rain  falls  from  year 
to  year  on  a  certain  soil.  In  the  course  of  time  there  is 
formed  at  this  point  an  accumulation  of  material  com- 
monly called  hardpan.  Under  a  light  rainfall,  on  a  clay 
soil,  the  hardpan  may  be  only  a  foot  or  two  below  the 
surface;  on  a  sandier  soil,  from  4  to  10  feet,  or  even  more, 
below  the  surface.  Students  of  arid  soils  often  estimate 
the  annual  precipitation  of  rain  and  snow  by  the  depth 
of  the  hardpan. 

Not  only  are  the  fine  clay  and  silt  particles  washed 
downward  by  the  rains.  Lime  and  other  similar  sub- 
stances are  dissolved  by  the  descending  water,  which 
cement  together  firmly  the  materials  of  the  hardpan. 
Such  calcareous  hardpans  are  often  so  hard  that  they 


SOIL  AS  WATER  RESERVOIR  33 

can  be  broken  only  by  explosives,  and,  usually,  in  the 
beginning  are  impervious  to  water. 

As  the  practice  of  irrigation  continues,  the  hardpan 
formed  by  the  natural  precipitation  is  softened,  the 
materials  of  which  it  is  made  are  distributed  over  larger 
soil  depths,  and  frequently  it  wholly  disappears, 
v  Under  vast  areas  of  the  soils  of  arid  regions,  and  not 
far  from  the  surface,  are  found  layers  of  shale  or  other 
stone.  These  were  deposited  by  geological  forces  upon 
the  soils  then  existing,  and  later,  through  ages,  new  soils 
were  deposited  upon  these  layers.  In  other  cases,  the 
original  rock  is  only  a  few  feet  below  the  surface.  Such 
hindrances  to  the  free  descent  of  water  cannot,  of  course, 
be  removed  by  frequent  irrigation./ 

An  impervious  layer  a  short  distance  below  the  sur- 
face, whether  of  a  temporary  or  permanent  nature, 
establishes  conditions  which  change  the  laws  of  distribu- 
tion of  water  in  soils  as  outlined  previously  in  this  chap- 
ter. When  the  irrigation  water,  in  its  descent,  encounters 
the  hardpan,  the  downward  movement  stops,  the  soil- 
moisture  film  thickens;  if  more  water  is  added,  water 
accumulates  on  the  hardpan  and  fills  the  soil  pores,  thus 
producing  an  undesirable  habitat  for  the  plant-roots, 
and  leads  to  serious  crop  injury. 

A  soil  underlaid  with  hardpan  is  always  in  danger  of 
being  water-logged,  for  the  tendency  is  to  apply  as  much 
water  to  such  soils  as  to  deeper  lands.  True,  as  will  be 
shown  later,  in  wet  soils  plants  use  more  water  than  in 
dry  ones.  Yet,  ordinarily,  more  water  is  added  than 
plants  can  use.  Moreover,  the  excess  of  water  in  the  soil 
is  a  positive  hindrance  to  successful  plant-growth.  Soils 
underlaid  with  hardpan  should  be  irrigated  more  mod- 
erately and  more  frequently  than  deeper  soils.  It  is  often 
c 


34  IRRIGATION  PRACTICE 

found  profitable  to  blast  occasional  holes  through  the 
hardpan  to  serve  as  outlets  for  the  excess  water  that 
stands  on  the  hardpans.  Such  holes,  to  be  effective, 
should  occur  frequently,  in  which  case  the  process 
becomes  very  expensive. 

27.  Effect   of   gravel. — When   the   soil   is   underlaid 
with  gravel,  or  if  gravel  seams  pass  through  it  within  10 
or  12  feet  of  the  surface,  the  normal  distribution  of  the 
soil   moisture   is   disturbed.    By  such  gravel    is   meant 
the  loose,  open  gravel  which  makes  the  soil  discontinuous. 
If  gravel  is  mixed  uniformly  with  the  soil  from  the  sur- 
face downward,  or  at  varying  depths,  the  soil  may  be 
looked  upon  as  being  continuous  so  far  as  the  distribu- 
tion of  water  is  concerned. 

When  water,  moving  downward,  reaches  a  layer  of 
loose  gravel,  the  descent  of  the  moisture  film  is  first 
arrested,  then  the  film  is  thickened  until  .the  lower  soil 
pores  are  filled,  and,  if  irrigation  is  continued,  gravita- 
tional water  drips  from  the  soil  into  the  gravel  below. 
The  water  which  thus  passes  into  the  gravel  can  not  move 
back  by  capillary  means,  and  usually  drains  away  into 
the  subsoil  and  is  lost  to  plant  use. 

Soils,  made  faulty  because  of  gravel  seams,  should 
therefore  be  irrigated  lightly.  Not  enough  water  should 
be  added  to  allow  any  part  to  move  into  the  subsoil. 
Under  such  conditions,  more  frequent  applications  of 
water  become  necessary.  On  the  benches  and  foothills, 
such  soils  are  of  frequent  occurrence. 

28.  Water  table  near  surface. — When  the  standing- 
water  table  is  within  reach  of  plant-roots,  heavy  irriga- 
tion should  be  avoided.    Just  enough  water  should  be 
added  to  keep  the  soil  moist  without  allowing  any  appre- 
ciable quantity  to  drain  into  the  ground  water. 


SOIL  AS  WATER  RESERVOIR  35 

29.  Soil  treatment. — A  deep,  continuous  soil  is  the 
best  under  irrigated  conditions.    On  such  a  soil  enough 
water  may  be  added  at  each  irrigation  to  leave  the  top 
foot   saturated   after   distribution   has   occurred.     This 
quantity  varies  usually  from  a  depth  of  5  to  8  inches  over 
the  whole  area.    To  make  more  rapid  the  entrance  of 
water  into  the  soil,  the  surface  should  be  kept  in  a  loose, 
absorptive  condition.    The  deeper  the  soil  is  plowed,  the 
greater  the  quantity  of  water  that  may  be  stored  in  a 
given  time,  in  the  top  soil,  to  move  gradually  downward 
into  the  subsoil.    Since  the  application  of  water  tends  to 
compact  the  soil,  it  becomes  necessary  to  stir  the  soil 
between  irrigations.     Such   stirring  not  only  makes   it 
easier  for  water  to  enter  the  soil;  it  also  reduces  the  loss 
from  evaporation. 

Soils,  which  within  10  or  12  feet  from  the  surface  are 
underlaid  with  hardpan  or  ground  water,  or  made  dis- 
continuous by  gravel  streaks  or  layers,  must  be  irrigated 
cautiously.  In  such  cases  the  quantity  of  water  to  be 
added  should  be  such  as  to  allow  only  a  thin  soil-mois- 
ture film  to  reach  the  hardpan,  ground  water  or  gravel. 
Small,  frequent  irrigations  must  be  the^rule  in  such  cases 
— smaller  and  more  frequent  as  the  faults  are  nearer 
the  surface. 

30.  How  much  water  can  be  stored. — It  is  clear  from 
the  statements  of  this  chapter  that  water  may  be  stored 
in  soils  to  considerable  depths  as  a  film  surrounding  the 
soil  particles  and  filling  the  capillary  spaces.   Since  water, 
whether  from   rain  or  irrigation,   is   ordinarily  applied 
intermittently,  it  is  important  to  know  how  much  of  the 
water  added  at  any  one  time  is  retained  by  soils  for 
the  use  of  plants. 

At  the  Utah  Station,  where  most  of  the  precipitation 


36 


IRRIGATION  PRACTICE 


comes  in  winter,  a  long  series  of  experiments  showed 
conclusively  that  in  the  spring  most  of  the  water  that 
fell  throughout  the  winter  was  held  in  the  upper  8  feet  of 
soil.  The  quantity  held  in  the  soil  section  varied  with 


FIG.  9.  Penetration  of  roots  of  prune  tree. 


SOIL  AS  WATER  RESERVOIR  37 

the  percentage  of  water  in  the  soil  in  the  fall.  If  the  soil 
went  into  the  winter  in  a  dry  condition,  practically  all 
of  the  winter  precipitation  was  found  in  the  spring  in  the 
upper  8  feet.  If,  on  the  other  hand,  the  soil  was  well 
filled  with  water  in  the  fall,  from  fallowing  or  fall  irriga- 
tion, a  relatively  small  quantity  of  the  winter  precipita- 
tion was  found  in  the  upper  8  feet  of  soil,  when  spring 
opened.  In  both  cases  the  soils  were  saturated  in  the 
spring.  That  is,  the  upper  foot  was  fully  saturated;  the 
percentage  diminished  steadily  with  each  succeeding 
foot  in  accordance  with  the  law  of  distribution  already 
explained.  It  was  clear  that  when  the  soil  was  fairly 
completely  saturated  in  the  fall,  the  winter  precipitation 
soaked  down  below  the  8-foot  limit.  During  six  years, 
1902  to  1907,  the  percentage  of  the  total  winter  pre- 
cipitation found  stored  in  the  soils  that  went  into  the 
winter  in  the  driest  condition  varied  from  63  to  96  per 
cent. 

This  teaches,  incidentally  that,  when  the  soil  is  sat- 
urated to  a  depth  of  10  to  12  feet,  there  is  not  an  advan- 
tage in  adding  more  water.  Therefore,  in  districts  where 
the  precipitation  comes  in  winter,  early  spring  irrigations 
may  have  little  value.  On  the  other  hand,  where  the 
winters  are  dry  and  the  summers  wet,  early  spring  irriga- 
tions should  prove  very  profitable. 

At  the  North  Platte  substation  of  the  Nebraska 
Station,  where  the  precipitation  comes  chiefly  in  early 
summer,  a  similar  series  of  experiments  were  conducted. 
It  was  found  that,  in  spite  of  the  water-dissipating  con- 
ditions of  summer,  from  40  to  50  per  cent  of  the  rain 
which  fell  from  May  1  to  September  1  was  stored  in  the 
soil  to  a  depth  of  6  feet  at  the  end  of  the  period.  Since  it 
was  evident  that  the  water  passed  below  the  6-foot  limit, 


38  IRRIGATION  PRACTICE 

it  is  probable  that  considerably  more  of  the  summer 
precipitation  would  actually  have  been  found  if  moisture 
determinations  had  been  made  to  greater  depths. 

Similar  results  were  obtained  from  the  irrigation 
experiments  of  the  Utah  Station.  Water  was  added  in 
varying  quantities  to  a  deep  loam  soil  already  well  filled 
with  water.  The  soil  was  sampled  to  a  depth  of  8  feet 
twenty-four  hours  after  irrigation.  The  results  for  one 
year  follow: 

Depth  of  water  applied,  in  inches     .    .    .  2.5  5.0  7.5 

Per  cent  of  the  water  added,  found  one 

day  after  irrigation 100.00         77.04         68.87 

Some  of  the  water  was  no  doubt  lost  by  evaporation; 
some  moved  below  the  8-foot  limit,  yet  from  69  to  100  per 
cent  of  the  total  quantity  added  was  found  to  be  stored 
in  the  soil,  for  the  use  of  plants,  one  day  after  irrigation. 

It  is  clear,  therefore,  that  water,  whether  of  rain  or 
irrigation,  may  be  stored  in  soils.  In  clay  soils,  with  fine 
particles  and  a  large  surface,  much  more  water  may  be 
stored  than  in  sandy  soils,  with  coarse  particles  and  a 
small  surface.  If  evaporation  is  prevented,  and  crops 
are  not  growing  on  the  soils,  such  stored  water  may 
remain  in  the  soil  for  long  periods  of  time.  If  the  water 
is  in  the  film  condition,  there  is  no  great  downward 
movement  after  equilibrium  is  once  restored. 

31.  Absorption  of  water  by  soils. — Water  storage  is 
best  accomplished  when  the  water  is  made  to  enter  the 
soil  quickly.  This  happens  when  the  top  soil  is  kept  in  a 
loose  condition  and  when  the  soil,  to  a  depth  of  several 
feet,  is  tolerably  moist.  If  the  surface  is  hard,  the  run- 
off is  large;  if  the  soil  is  dry,  the  downward  penetration 
is  slow. 


SOIL  AS  WATER  RESERVOIR  39 


REFERENCES 

ALWAY,  F.  J.,  and  CLARK.  A  Study  of  the  Movement  of  Water 
in  a  Uniform  Soil  under  Artificial  Conditions.  Nebraska  Experi- 
ment Station,  Twenty-fifth  Annual  Report,  p.  246  (1912). 

BURR,  W.  W.  Storing  Moisture  in  the  Soil.  Nebraska  Experiment 
Station,  Bulletin  No.  114  (1910). 

LEATHER,  J.  W.  Water  Requirements  of  Crops  in  India.  Part  II. 
Agricultural  Research  Institute,  Pusa,  Memoirs  of  the  Depart- 
ment of  Agriculture  in  India,  Chemical  Series,  Vol.  I,  No.  10 
(1911). 

LOUGHRIDGE,  R.  H.  Distribution  of  Water  in  the  Soil  in  Furrow 
Irrigation.  United  States  Department  of  Agriculture,  Office 
of  Experiment  Stations,  Bulletin  No.  203  (1908). 

WIDTSOE,  J.  A.  Dry-Farming  (1911).  Chapter  VII,  Storing  Water 
in  the  Soil. 

WIDTSOE,  J.  A.  The  Storage  of  Winter  Precipitation  in  Soils.  Utah 
Experiment  Station,  Bulletin  No.  104  (1908). 

WIDTSOE,  J.  A.,  and  MCLAUGHLIN,  W.  W.  The  Movement  of 
WTater  in  Irrigated  Soils.  Utah  Experiment  Station,  Bulletin 
No.  115  (1912). 


CHAPTER  IV 
SAVING  WATER  BY  CULTIVATION 

WATER  added  to  the  soil  by  the  natural  precipitation 
or  by  irrigation  is  disposed  of  in  two  chief  ways :  One  part 
runs  off  the  land;  another  part  soaks  into  the  ground. 

The  water  which  soaks  into  the  soil  may  be  disposed 
of  in  three  ways:  (1)  Immediately  after  water  has  entered 
the  soil,  evaporation  begins  at  the  surface  and,  in  time, 
if  not  checked,  the  water  in  the  greater  depths  will  be 
brought  to  the  surface,  to  be  returned  to  the  air  in  the 
form  of  water  vapor.  (2)  If  an  excess  of  water  has  been 
applied,  another  part  sinks  below  the  reach  of  the  plant 
roots  and  may  connect  with  the  country  drainage,  and 
thus  be  lost  to  the  farmer.  (3)  A  part  remains  in  the 
soil  and  supplies  the  plant  with  the  water  needed  in  its 
growth. 

The  vital  thing  in  irrigation  practice  is  to  bring  the 
water  into  the  soil  properly  and  to  keep  it  stored  there, 
within  reach  of  the  roots,  until  it  is  needed  by  the  plant. 

32.  The  run-off. — The  run-off  collects  in  hollows  or 
cuts  channels  to  connect  it  with  the  larger  streams  of 
surface  water.  The  quantity  of  water  thus  lost  often 
forms  a  very  large  part  of  the  total  water  added  by  the 
natural  precipitation  or  by  irrigation.  To  prevent  this, 
it  is  necessary  to  keep  the  top  soil  in  a  loose,  open  con- 
dition, so  that  the  water  that  falls  upon  it  may  be 
absorbed  quickly.  Where  the  major  part  of  the  precipi- 
tation comes  during  the  winter  or  spring,  the  best  way  of 

(40) 


SAVING  WATER  BY  CULTIVATION  41 

accomplishing  this  is  to  plow  the  land  in  the  fall  and, 
unless  fall  crops  are  planted,  to  allow  it  to  lie  in  a  rough 
state  throughout  the  winter.  Where  the  precipitation 
comes  largely  during  the  summer  and  spring,  it  is  much 
more  difficult,  because  of  the  growing  crops,  to  keep  the 
top  soil  in  a  condition  to  absorb  water  readily. 

Much  water  is  nearly  always  lost  at  the  time  of  thaw- 
ing and  melting  snow.  In  such  districts  all  furrows  and 
rows  of  plants  should  be  made  to  conform  with  the  slope 
of  the  land.  A  furrow  plowed  up  and  down  a  gentle  slope 
forms  an  admirable  channel  for  the  escape  of  water,  while 
a  furrow  plowed  at  right  angles  to  the  slope  tends  to  catch 
and  to  hold  back  the  water  which  flows  downward. 
This  is  also  true  with  regard  to  planting.  Drill  culture 
is  now  the  only  acceptable  method  of  planting;  and  it  is 
always  desirable,  from  the  point  of  view  of  preventing  the 
run-off,  to  plant  the  rows  of  crops  at  right  angles  to  the 
general  slope  of  the  land.  Each  row  then  tends  to  pre- 
vent excessive  run-off. 

In  irrigation,  the  loss  due  to  run-off  is  frequently  a 
very  serious  matter.  When  water  is  applied  by  the 
flooding  method,  it  is  relatively  easy  to  control  the  run- 
off by  building  dikes  around  the  field.  In  fact,  some  kind 
of  diking  is  usually  thrown  up  around  large  fields,  when- 
ever water  is  applied  by  the  flooding  method.  The  vari- 
ous systems  of  irrigation  by  flooding  differ  chiefly  in  the 
means  devised  for  preventing  the  surface  loss  of  water. 
If  no  diking  is  used,  the  lower  end  of  the  field  is  usually 
crossed  by  a  ditch,  which  receives  the  waste  water  and 
carries  it  to  some  other  field. 

In  the  furrow  method  of  irrigation  it  is  very  difficult, 
if  not  impossible,  to  prevent  wholly  the  run-off.  By  the 
furrow  method,  water  is  usually  applied  at  one  end  of  the 


42  IRRIGATION  PRACTICE 

field  and  allowed  to  run  down  long  furrows,  often  several 
feet  apart.  It  is  practically  impossible  so  to  regulate  the 
stream  that  all  the  water  is  absorbed  just  at  the  end  of 
each  furrow.  In  fact,  if  this  is  attempted  by  using  a  very 
small  stream,  it  means  that  the  upper  end  will  receive  a 
very  large  quantity  of  water,  while  the  lower  end  will  be 
relatively  dry  and  often  without  a  sufficient  supply  of 
moisture  for  abundant  plant-growth.  If  a  large  stream  is 
used,  the  whole  furrow  is  given  a  thorough  wetting,  but  a 
large  quantity  of  water  is  wasted  at  the  end  of  the  furrow. 
This  waste  water  is  usually  received  by  a  transverse  ditch 
and  used  on  some  lower  field.  To  reduce  the  run-off  and, 
at  the  same  time,  give  each  furrow  a  sufficient  irrigation, 
the  best  plan  seems  to  be  to  use  a  small  stream  and  a 
rather  short  furrow,  repeating  the  furrow  below  as  many 
times  as  may  be  necessary.  The  shorter  the  furrow  is, 
the  more  thoroughly  and  uniformly  may  water  be  applied 
to  the  soil. 

In  any  event,  the  run-off  water  must  be  carefully  and 
skilfully  used  on  lower  fields.  The  run-off  presents  a 
problem  which  must  be  solved  in  its  own  peculiar  way  on 
each  individual  farm.  No  general  rules  can  be  laid  down 
for  using  the  run-off,  since  the  layout  of  one  farm  is 
generally  different  from  that  of  any  other. 

33.  The  upward  movement  of  water. — Under  methods 
of  irrigation  that  use  water  in  moderation,  very  little 
water  drains  below  the  zone  of  root-action,  yet  under 
the  most  favorable  conditions  water  may  move  upward 
and  be  lost  from  the  soil  surface.  The  movement  of 
water  is  usually  from  the  thick  to  the  thin  film,  that  is, 
from  the  moister  to  the  drier  parts  of  the  soil.  When, 
therefore,  a  soil  dries  at  the  surface,  there  is  a  steady 
upward  movement  of  water  from  particle  to  particle  to 


SAVING  WATER  BY  CULTIVATION  43 

supply  that  lost  by  evaporation  at  the  top  and  to  place 
the  remaining  water  in  full  equilibrium  with  all  active 
forces.  Such  loss  of  water  is  felt  to  the  full  depth  of  soil 
concerned  in  plant-growth. 

As  evaporation  proceeds  from  the  top  soil,  the  water 
in  every  soil  layer  diminishes  to  the  full  depth  of  root- 
action.  The  process  may  be  likened  roughly  to  the  behav- 
ior of  cotton  packed  loosely  in  a  box.  If  a  small  quantity 
is  removed  from  the  top,  the  remainder  expands  and 
fills  the  box  again,  the  difference  being  that  the  whole 
mass  is  looser  from  the  top  downward  than  it  was  before. 
So,  after  evaporation  has  occurred,  and  water  has  moved 
upward  to  replace  the  loss,  there  is  a  thinner  soil-water 
film  throughout  the  soil.  This  process  may  go  on  until 
the  soil-water  film  has  been  reduced  to  the  minimum 
thickness  that  allows  capillary  movement.  When  this 
degree  of  dryness  has  been  reached,  it  does  not  follow  that 
the  film  is  of  the  same  thickness  at  every  point  to  the  full 
depth  involved.  On  the  contrary,  the  lower  layers,  to  a 
depth  of  8  to  10  feet,  contain  more  water  than  do  the 
upper  soil  layers.  At  first,  as  evaporation  proceeds,  the 
tendency  is  to  distribute  the  water  evenly  over  the  soil 
sections  below  the  upper  one,  which  is  immediately 
exposed  to  the  atmosphere  and  therefore  always  drier. 
As  the  lento-capillary  point  is  approached,  the  upward 
movement  becomes  more  and  more  sluggish;  and,  in 
fact,  it  is  ordinarily  very  difficult  to  reduce  the  lower 
soil  layers  below  this  point,  though  the  upper  layers  may 
be  brought  considerably  lower  in  their  moisture  content. 
When  living  plant-roots  fill  the  soil,  this  distribution 
does  not  hold,  for  the  roots  draw  moisture  directly  from 
the  soil,  and  the  percentage  of  soil  moisture  is  in  inverse 
proportion  to  the  distribution  of  the  roots. 


44 


IRRIGATION  PRACTICE 


To  stop  the  upward  movement  of  soil  water  due  to 
surface  evaporation  is  a  chief  consideration  of  a  system 
of  irrigation-farming  in  which  economy  in  the  use  of 
water  is  a  vital  factor. 

34.  Intensity  of  evaporation. — It  is  well  known  that 
water  evaporates  into  the  air  whenever  the  air  is  not 
fully  saturated  with  water  vapor.  Under  the  conditions 


FIG.  10.  Evaporation  usually  exceeds  rainfall. 

prevailing  over  the  earth's  surface,  the  air  is  always 
unsaturated.  In  arid  regions  the  air  is  very  dry,  as  is 
well  shown  by  the  high  heat  that  may  be  endured  in 
such  places,  due  to  the  rapid  evaporation  of  perspiration 
into  the  dry  air. 

The  rate  of  evaporation  from  water  surfaces  is  much 
larger  than  commonly  believed.  Briggs  and  Belz  have 
sought  out  all  available  records  in  various  sections  of  the 
United  States,  of  the  quantities  of  water  that  will  evapo- 
rate from  a  free-water  surface  during  the  six  summer 
months,  April  to  September  inclusive.  A  summary  of 
their  findings  is  presented  in  the  following  table: 


SAVING  WATER  BY  CULTIVATION 


WATER  LOST  (IN  INCHES)  BY  EVAPORATION  FROM  A  FREE-WATER 
SURFACE  FROM  APRIL  TO  SEPTEMBER,  INCLUSIVE 


State 


Highest 


Lowest 


Arizona 56.2 

California  i_. 71.8 

Colorado     .1 61.6 

Nevada 51.0 

New  Mexico 54.6 

Utah 42.0 

Washington 27.6 

Wyoming 39.4 

Kansas 59.9 

Michigan 32.1 

Montana 32.6 

Nebraska 41.3 

North  Dakota 31.4 

South  Dakota 38.0 

Texas 54.6 

Wisconsin 28.8 

Massachusetts 28.6 

New  Jersey 29.5 

New  York 26.7 

Ohio    .  24.6 


54.2 
21.2 
29.3 
39.9 
40.1 
30.7 


45.2 
30.2 

34.8 
29.8 
33.7 
45.7 
26.9 

25.8 


This  table  is  not  complete,  but  it  shows  unmistak- 
ably, first,  that  evaporation  is  much  greater  in  the  arid 
than  in  the  humid  region,  and,  second,  that  in  both 
humid  and  arid  regions  the  evaporation  from  a  free-water 
surface,  during  the  six  summer  months,  is  considerably 
more  than  the  total  quantity  of  irrigation  water  that 
should  properly  be  applied  in  any  one  year.  In  the  arid 
states,  as,  for  instance,  California,  with  its  high  evapora- 
tion record  of  nearly  72  inches,  several  times  the  quantity 
of  water  that  should  be  applied  in  irrigation  may  easily 
be  evaporated  into  the  air  during  the  growing  season. 

From  soils  kept  wet  at  the  surface,  evaporation  goes 
on  even  faster  than  from  a  water  surface.  For  instance, 


46  IRRIGATION  PRACTICE 

Fortier  reports  an  average  weekly  evaporation  from  a 
wet  soil  of  4.75  inches  and  from  a  water  surface  placed 
under  like  conditions  only  1.88  inches — two  and  one-half 
times  as  much.  The  explanation  of  this  must  of  course 
be  sought  in  the  higher  temperature  of  the  soil  due  to  a 
lower  specific  heat  and  a  higher  absorptive  capacity 
for  heat. 

This  strong  tendency  of  water  to  return  to  the  air 
by  way  of  evaporation  makes  it  fundamentally  impor- 
tant to  devise  and  put  into  operation  methods  that  will 
prevent,  to  the  largest  possible  degree,  this  form  of  the  dis- 
sipation of  water.  (Fig.  10.) 

35.  Conditions  determining  evaporation. — Many  fac- 
tors are  concerned  in  the  evaporation  of  water  from  the 
surface  of  water  or  any  moist  substance  such  as  an  irri- 
gated soil.  These  may  be  classified  as  follows: 

1.  Nature  of  soil. 

(a)  Physical. 
(6)  Chemical, 
(c)  Depth. 

2.  Meteorological  conditions. 

(a)  Temperature. 
(6)  Sunshine. 

(c)  Relative  humidity/ 

(d)  Winds. 

(e)  Showers. 

3.  Initial  percentage  of  water. 

4.  Condition  of  top  soil. 

(a)  Plowing. 
(6)  Cultivation. 

(c)  Rolling. 

(d)  Packing 


SAVING  WATER  BY  CULTIVATION  47 

The  nature  of  the  soil  is  of  considerable  importance. 
The  finer  the  texture  of  the  soil,  the  more  rapidly  does 
the  water  move  upward  to  be  changed  into  vapor.  The 
darker  the  color  of  the  soil,  the  more  rapid  the  evapora- 
tion; for  dark-colored  soils  absorb  the  heat  of  the  sun- 
shine much  more  quickly  than  do  lighter-colored  ones 
such  as  characterize  the  arid  region.  The  richer  the  soil 
is  in  soluble  salts,  the  slower  is  the  evaporation  of  water 
/  rato-%he— airT^-For  that  reason,  evaporation  from  alkali 
lands  is  slow.  The  rate  of  evaporation  is  more  rapid 
from  a  deep  than  from  a  shallow  soil,  for  a  given  loss  of 
water  does  not  so  greatly  reduce  the  percentage  of  mois- 
ture in  a  deep  as  in  a  shallow  soil. 

Meteorological  conditions  determine  very  largely 
the  rate  of  evaporation  of  water  from  soils.  Of  these, 
temperature  is  most  important.  The  higher  the  tempera- 
ture, the  more  rapid  is  the  conversion  of  water  into  water 
vapor.  Of  almost  equal  importance  is  the  intensity  and 
quantity  of  sunshine.  Much  more  water  is  lost  from  a 
wet  soil  on  a  sunny  day  than  on  a  cloudy  one.  Shade  is 
extremely  effective  in  checking  evaporation.  In  the  Utah 
work,  a  saving  of  25  per  cent  of  the  water  evaporated 
was  effected  when  the  soil  was  shaded;  and,  in  all  proba- 
bility, as  the  temperature  is  very  much  lower  in  the 
shade,  an  even  higher  degree  of  saving  may  be  effected. 
Frequently,  a  high  temperature  and  much  sunshine  go 
together,  so  that  their  effects  are  felt  at  the  same  time. 
The  drier  the  air,  the  more  rapidly  will  the  air  take  up 
water  vapor.  In  the  arid  region,  the  relative  humidity 
of  the  air  is  low,  and  evaporation  goes  on,  as  has  been 
shown,  much  more  rapidly  than  in  humid  sections. 
Winds,  likewise,  exert  a  strong  drying  effect  on  soils, 
especially  in  districts  where  the  air  is  relatively  dry.  The 


48 


IRRIGATION  PRACTICE 


water,  as  it  evaporates  from  the  soil,  saturates  the  air 
immediately  above  the  soil  surface;  and  thus  evapora- 
tion is  diminished.  Winds  remove  this  layer  of  saturated 
air,  and  the  rate  of  evaporation  is  increased.  Summer 
showers,  likewise,  by  establishing  capillary  connection 
with  the  lower  soil  layers,'  hasten  evaporation. 

Finally,  the  wetter  the  soil  is  at  the  surface,  the  more 
rapidly  is  water  evaporated  from  it.    This  vitally  impor- 


r* 

i 

j 

\ 

f 

/ 

"\ 

,' 

\ 

\ 

/ 

r 

X> 

/ 

* 

\ 

t 

/ 

\ 

\ 

/ 

\ 

\ 

1- 

/ 

\ 

\ 

/ 

i  \ 

X 

*$* 

• 

\ 

\ 
\ 

f,' 

7 

\ 

\ 

.,* 

I 

\ 

.  \ 

\ 

/- 

7 

V 

v 

>  . 

*H~T7 

\ 

/ 

/ 

/> 

\ 

v 

LjeL 

/ 

\ 

I^L 

/ 

•^ 

Jan  Feb  Mar  Apr  May  June  July  Aug  SeptOct,  NoVDec.Jjm  Feb  Mar  Apr  May  June  July  Aug  SeptOct  No*  Dec 
1904                                                                        ,905 

FIG.  11.  Relation  beween  temperature  and  evaporation  (Tulare,  Calif.). 

tant  principle  was  observed  in  the  Utah  work,  and  has 
been  confirmed  by  Whitney  and  Cameron  and  by  For- 
tier.  This  law  of  the  initial  percentage  declares  that  the 
evaporation  of  water  from  a  soil  surface  varies  as  the 
initial  percentage  of  soil  moisture, — that  is,  the  mois- 
ture at  the  beginning  of  the  test. 

The  three  most  important  factors  in  determining  the 
evaporation  of  water  from  a  soil  are  undoubtedly  the 
average  temperature,  the  relative  humidity  of  the  air, 
the  wind,  and  the  percentage  of  water  held  by  the  soil, 


SAVING  WATER  BY  CULTIVATION  49 

The  temperature  cannot  be  controlled,  effectively,  by  the 
farmer;  neither  can  the  relative  humidity;  and,  if  the  land 
is  to  produce  the  largest  and  best  crops,  there  must  be  in 
the  soil  a  fair  abundance  of  water.  To  diminish  the  rate 
of  evaporation  by  controlling  these  three  factors  seems, 
therefore,  almost  hopeless.  The  control  must  come  from 
the  proper  treatment  of  the  top  soil.  (Fig.  11.) 

36.  Mulching  to  check  evaporation. — It  was  observed 
many  years  ago,  that  evaporation  of  water  from  soils 
may  be  quite  effectively  stopped  by  covering  the  soil 
loosely  with  straw,  manure,  litter  of  any  kind  or  loose 
soil.  This  method  has  been  tried  out  practically  in  so 
many  countries  and  by  so  many  investigators  that  there 
can  be  no  question  about  its  effectiveness. 

Fortier  recently  re-examined  the  matter,  under  the 
climatic  conditions  of  the  irrigated  sections  of  the  United 
States,  and  found  that  a  covering  of  sand,  if  of  proper 
depth,  applied  to  the  soil  immediately  after  irrigation, 
could  be  made  to  reduce  the  evaporation  to  less  than  2 
per  cent  of  the  water  applied.  In  earlier  days,  it  was 
advocated  rather  largely  that  straw  and  other  litters  be 
placed  upon  the  soil  to  prevent  evaporation.  This  method, 
however,  is  too  expensive  to  be  of  wide  application. 

The  method  of  today  is  to  stir  the  top  soil  with  proper 
implements.  The  process  is  called  cultivation.  The 
layer  of  loose  dirt  which  is  thus  left  upon  the  soil  hinders 
very  effectively  the  movement  of  soil  water  into  the 
atmosphere.  In  the  Utah  work  it  was  found  that,  by 
cultivation,  an  infertile  clay  soil  lost  only  63  per  cent  of 
the  quantity  lost  by  the  non-cultivated  soil;  a  fertile 
clay  loam,  13  per  cent,  and  a  loose  sandy  soil,  34  per  cent. 
Fortier  found  that  by  thorough  cultivation  of  a  southern 
California  soil  the  loss  by  evaporation  could  be  reduced 
D 


50  IRRIGATION  PRACTICE 

to  less  than  half  of  that  from  a  non-cultivated  soil.  Scores 
of  other  investigators  have  demonstrated  that  the  mulch 
formed  by  cultivation  reduces  largely  the  evaporation. 

This  saving,  due  to  mulching,  is  easily  understood. 
As  has  been  explained,  soil  moisture  is  held  as  a  film 
around  the  soil  particles.  Water  moving  toward  the  soil 
surface  must  pass  from  particle  to  particle  through  the 
narrow  films  at  the  points  of  contact  of  the  soil  particles. 
The  smaller  or  the  fewer  these  points  of  contact,  the  more 
difficult  is  the  upward  movement  of  the  water.  If  water 
were  passing  through  a  large  tube  into  several  smaller 
tubes,  the  flow  of  water  would  be  retarded.  When  the  top 
soil  is  loosened,  the  points  of  contact  between  the  loose  soil 
above  and  the  compacted  soil  below  become  reduced. 
At  the  zone  of  loose  earth,  the  ascending  water  finds  it 
difficult  to  pass  through  the  fewer  points  of  contact,  and 
at  the  same  time  to  maintain  its  rate  of  flow.  The  more 
thoroughly  the  soil  is  cultivated,  that  is,  the  fewer  the 
points  of  contact,  the  more  difficult  will  the  movement 
become,  and  the  more  greatly  will  the  evaporation 
be  reduced. 

Likewise,  as  a  soil  becomes  dry,  the  flow  of  moisture 
through  it  is  lessened.  This  is  clearly  understood  when  it 
is  recalled  that  a  dry  soil  means  a  soil  with  very  thin 
moisture  films  around  the  particles.  Water  passing 
through  thin  films  encounters  much  friction,  and  the 
rate  of  flow  is  diminished.  Stirring  the  top  soil  tends  to 
dry  it  out  very  rapidly,  and  to  leave  a  very  dry  mulch, 
through  which  water  can  pass  only  with  difficulty.  Culti- 
vation, therefore,  retards  evaporation  by  breaking  the 
points  of  contact  between  the  upper  and  lower  soil  layers 
and  by  drying  out  the  loosened  top  layer. 

It  is  true  that  from  the  surface  of  every  soil  particle, 


SAVING  WATER  BY  CULTIVATION 


51 


at  any  depth,  water  is  evaporated,  until,  if  the  soil  is 
moist,  the  pores  of  the  soil  are  filled  with  air  saturated 
with  vapor  water.  This  saturated  soil  air  moves,  how- 
ever, very  slowly  into  the  atmosphere.  Buckingham 
has  shown  that  water  vapor  escapes  from  the  soil  air 
only  by  the  slow  process  of  diffusion;  that  is,  the  particles 
of  water  vapor  find  their  way,  one  by  one,  into  the  atmos- 
phere, while  there  is  a  corresponding  movement  of 
atmospheric  gases  into  the  soil  air.  This  interchange  of 
gases  between  the  soil  air  and  the  atmosphere  is  so  small 
as  to  be  of  little  or  no  consequence  in  the  loss  of  soil  water 


Fia.  12.  Evaporation  losses  from  soils  protected  with  mulches  of  different  depths. 

by  evaporation.   Practically  all  soil  water  is  lost  by  evap- 
oration at  the  soil  surface. 

Buckingham  has  shown,  also,  that  very  little  water 
is  lost  by  direct  evaporation  2  inches  below  the  surface. 
From  below  a  12-inch  layer  of  dry  soil  the  evaporation- 


52  IRRIGATION  PRACTICE 

loss  is  insignificant,  amounting  at  most  to  only  1  inch  of 
rainfall  in  six  years. 

The  most  effective  method  of  checking  evaporation 
from  the  soil  is  to  stir  the  top  soil  thoroughly  with  any 
one  of  the  many  kinds  of  cultivators  now  found  on  the 
market  and  built  especially  for  the  purpose.  (Fig.  12.) 

37.  Self -mulching  soils. — Under  arid  conditions, 
some  soils  possess  a  self-mulching  power.  The  abundant 
sunshine,  high  temperature  and  low  relative  humidity 
of  arid  sections,  cause  a  very  rapid  evaporation.  After 
an  irrigation  on  a  very  hot  summer  day  the  top  soil  may 
be  dried  out  so  rapidly  that  the  lower  soil  lasers  cannot 
send  moisture  upward  in  time  to  supply  the  loss.  Under 
such  conditions  the  evaporation  is  automatically 
decreased.  The  dry  top  soil,  thus  induced,  is  an  effec- 
tive check  upon  the  upward  movement  of  water.  This 
may  be  one  explanation  of  the  fact  that  in  many  virgin 
arid  lands  much  of  the  rainfall  remains  stored  for  months 
at  a  time.  Added  to  this  is  another  condition  of  frequent 
occurrence.  Arid  soils  are,  as  a  rule,  rich  in  lime.  In  some 
cases  the  calcareous  substances  of  arid  soils  make  up  one- 
fourth  to  one-half  of  the  soil  itself.  Such  soils,  as  they 
dry  out,  become  loose.  It  frequently  happens,  there- 
fore, that  when  such  a  soil,  after  an  irrigation,  is  dried 
out  by  rapid  evaporation,  the  surface  layer  falls  into  a 
natural  mulch  which  is  fairly  effective  in  stopping  evapo- 
ration. Buckingham  reports  an  interesting  experiment, 
in  which  he  found  that  the  rapid  evaporation  due  to  arid 
conditions  so  dried  out  the  top  soil  that  the  loss  of  water 
in  a  year  was  only  11.2  inches  as  against  51.6  inches  from 
a  similar  soil  under  humid  conditions  which  permitted  a 
slow  but.  steady  evaporation. 

The  stirring  of  such  self-mulching  soils  does  not  always 


SAVING  WATER  BY  CULTIVATION  53 

save  soil  moisture.  In  the  Utah  work  such  a  soil  was 
found,  from  which  one  and  one-half  times  more  water 
was  lost  during  the  growing  season  when  cultivation  was 
practised.  The  natural  mulching  of  this  soil  permitted 
the  lowest  evaporation  of  a  large  series  of  tests  with 
several  varieties  of  soil.  Nevertheless,  even  on  such  soil, 
the  stirring  of  the  soil  carried  with  it  other  beneficial 
results  of  high  value  to  crops.  That  is,  even  though 
cultivation  on  such  soils  may  cause  a  greater  loss  of  water, 
the  soil  becomes  able  by  the  cultivation  to  produce  more 
dry  matter  with  the  water  actually  at  its  disposal.  This 
was  well  brought  out  in  the  Utah  work,  for  the  self- 
mulching  soil  produced  a  crop  14  per  cent  larger  on  the 
cultivated  areas. 

Self-mulching  soils  are  not  plentiful,  and  too  much 
reliance  should  not  be  placed  upon  them.  The  irrigation 
farmer  is  safe  only  when  he  cultivates  his  soils  thoroughly 
and  frequently  throughout  the  season. 

38.  Time  of  cultivation. — The  rate  at  which  water 
soaks  into  a  soil  depends  largely  upon  the  physical  con- 
dition of  the  land.  If  the  soil  is  coarse  and  loose,  the  down- 
ward movement  is  rapid  ;tif  fine  and  compact,  the  down- 
ward movement  is  slow.  In  any  case  the  top  soil  remains 
saturated  or  too  wet  for  cultivation  during  several  hours, 
or  days,  after  an  irrigation.  A  sand  or  loam  soil  may  often 
be  cultivated  within  one  or  two  days  after  irrigation;  but, 
on  a  clay  soil,  this  cannot  be  done  until  three  to  seven 
days  after  irrigation.  During  this  period  before  cultiva- 
tion, when  the  top  soil  remains  moist,  evaporation  losses 
occur  very  rapidly.  In  fact,  from  one-fifth  to  one-third 
of  the  loss  due  to  evaporation  throughout  a  three-  or 
four-week  period  occurs  before  the  cultivator  can  be 
applied  to  form  a  protective  soil  mulch. 


54  IRRIGATION  PRACTICE 

The  chief  protection  against  the  great  losses  immedi- 
ately after  irrigation  and  before  cultivation  is  possible, 
is  a  loose,  spongy  top  soil  that  absorbs  the  water  the 
moment  it  is  applied  and  permits  it  to  soak  deeply  into 
the  soil  away  from  the  immediate  action  of  the  sun's 
rays.  Occasionally  it  may  be  profitable  to  scatter  a 
mulch  of  some  kind  over  the  soil,  immediately  after  an 
irrigation,  but  this  is  of  extremely  limited  application. 
If  water  is  applied  by  sub-surface  methods  this  pre- 
cultivation  loss  may  be  prevented,  but  sub-irrigation  is 
seldom  profitable  except  in  districts  were  natural  sub- 
irrigation  is  feasible. 

The  soil  should  be  cultivated  just  as  soon  as  it  is  pos- 
sible to  do  so  after  an  irrigation,  without  doing  injury  to 
the  soil.  If  cultivation  is  performed  too  soon  after  irriga- 
tion there  is  danger  of  leaving  the  top  soil  puddled  or 
in  an  otherwise  undesirable  physical  condition  for  plant- 
growth.  By  too  early  cultivation  a  soil  may  be  perma- 
nently injured  for  the  season  or  even  for  several  seasons. 
The  farmer  who  cultivates  too  early,  and  thereby  leaves 
the  top  soil  in  a  poor  physical  condition,  ultimately  loses 
more  than  does  he  who  permits  evaporation  to  go  on  a 
day  longer,  to  make  sure  that  the  soil  is  in  the  right  con- 
dition for  cultivation.  Whenever  the  soil  is  dry  enough 
to  support  the  man  and  horse  with  the  cultivating  tool, 
it  is  usually  safe  to  begin  cultivation. 

On  the  other  hand,  it  must  be  said  that,  in  the  great 
majority  of  cases,  the  farmer  permits  evaporation  to  go 
on  many  days  after  the  time  of  safe  cultivation  has  been 
reached.  Few  fields  are  injured  from  too  early  cultiva- 
tion. Over  the  whole  irrigated  area,  the  farmers  have 
looked  upon  cultivation  as  an  incidental  matter,  because 
they  have  not  realized  the  tremendously  large  quanti- 


SAVING  WATER  BY  CULTIVATION 


55 


ties  of  water  that  may  be  lost  from  the  soil  by  evapora- 
tion. The  magnitude  of  such  losses  is  well  shown  in  the 
following  typical  results  taken  from  the  Utah  work.  The 
soil  at  the  beginning  of  each  test  contained  practically 
17.5  per  cent  of  water. 


Days  after  irrigation 

Pounds  of  water 
lost  per 
square  foot 

Tons  of  water 
lost  per  acre 

Loss  as  depth 
of  water  in 
inches 

One  to  seven    

7.54 

164.22 

1.45 

One  to  fourteen 

10.08 

219.54 

1.93 

One  to  twenty-one      .... 

14.09 

307.09 

2.71 

During  the  first  seven  days  after  irrigation,  a  quan- 
tity of  water  equivalent  to  nearly  1.5  inches  was  lifted 
from  the  soil  by  the  power  of  the  sunshine;  during  the 
first  fourteen  days,  nearly  2  inches,  and,  during  the  first 
twenty-one  days  about  2%  inches.  Fortier  and  Beckett 
found  that  during  a  twenty-eight-day  period  after  irri- 
gation a  non-cultivated  soil  lost  2.13  inches  of  water,  of 
which  about  .8  of  an  inch  or  nearly  40  per  cent  was  lost 
during  the  first  three  days  after  irrigation,  before  culti- 
vation could  begin.  Such  great  losses  in  an  arid  section 
justify  every  effort  of  the  farmer  to  conserve  the  soil 
moisture  by  cultivation, — and  it  should  be  done  as  early 
as  possible  so  that  the  water  saving  may  be  large. 

39.  Depth  of  cultivation. — The  depth  to  which  a  soil 
is  cultivated,  that  is,  the  thickness  of  the  soil  mulch 
produced,  determines  the  rate  of  evaporation  and  there- 
fore the  quantity  of  soil  moisture  that  may  be  saved. 
This  is  only  to  be  expected,  for  the  thicker  the  dry  mulch 
above  the  moist  soil  from  which  evaporation  proceeds, 
the  greater  is  the  hindrance  offered  to  the  diffusion  of 


56 


IRRIGATION  PRACTICE 


water  vapor  into  the  atmosphere,  and  the  less  effectively 
can  the  sunshine  heat  the  evaporating  surface.  The 
best  investigations  on  this  subject  are  those  recently 
conducted  by  Fortier,  and  Fortier  and  Beckett,  under 
true  arid  conditions.  These  experiments  were  made  at 
five  different  points  in  the  arid  region — in  California, 
Montana,  Nevada,  Washington  and  New  Mexico — so  that 
the  validity  of  the  results  could  be  checked  under  the 
varying  climatic  conditions  of  the  irrigated  region. 
Immediately  after  each  irrigation,  "fine,  dry,  granu- 
lated soil  mulches,"  of  different  depths,  were  placed  upon 
the  soil,  and  the  water  losses  were  determined  during  a 
period  of  four  weeks.  Some  of  the  average  results  are 
as  follows: 


Depth  of  mulch  in 
inches 

Loss  of  water 
during  28  days 
in  inches 

Per  cent 

None 

1.75 

100.0 

3 

0.78 

42.3 

6 

0.34 

19.4 

9 

0.22 

12.5 

The  thicker  the  mulch  placed  upon  the  soil  the  smaller 
was  the  evaporation,  varying  from  1.75  inches,  when  no 
mulch  was  applied,  to  .22  inch  or  12.5  per  cent,  when  a 
9-inch  mulch  was  spread  over  the  soil  surface. 

In  another  series  of  experiments,  a  10-inch  mulch 
practically  stopped  evaporation.  When  the  mulch  is 
made  by  cultivation,  similar  results  are  obtained,  the 
difference  being  the  loss  immediately  after  irrigation 
and  just  before  cultivation,  discussed  above. 

It  may  be  said  safely  that  the  deepest  cultivation  is 
the  most  effective  for  the  checking  of  evaporation  from 


58  IRRIGATION  PRACTICE 

irrigated  soils.  However,  in  practice  it  is  often  difficult 
to  cultivate  below  a  depth  of  approximately  6  inches, 
unless  the  soil  is  of  the  right  character  and  proper  imple- 
ments are  used.  The  greatest  depth  to  which  any  soil 
may  be  cultivated  must  be  determined  by  the  individual 
farmer.  There  has  been  considerable  opposition  to  deep 
cultivation  on  the  ground  that  it  tends  to  destroy  the 
roots  which  feed  in  the  upper  layers  of  the  soil.  Some 
plants  are  naturally  more  shallow-rooted  than  are  others, 
but  an  important  thing  in  all  arid  agriculture  is  to  com- 
pel plant-roots  to  go  deeply  into  the  soil.  Shallow-rooted 
plants,  under  conditions  of  irrigation,  usually  indicate 
that  the  farmer  has  used  water  unwisely  by  irrigating 
too  frequently  or  too  heavily.  Proper  irrigation,  moderate 
in  quantity  and  at  proper  intervals,  causes  practically 
all  the  ordinary  cultivated  plants  to  strike  their  roots 
deeply  into  the  soil — so  deeply  that  no  damage  results 
from  the  deep  cultivation  indicated  by  the  experiments 
here  recorded.  In  many  sections  of  the  West,  notably 
in  the  orange  districts  of  southern  California,  where  the 
rainfall  is  light  and  irrigation  water  scarce,  deep  culti- 
vation has  become  a  general  practice  in  spite  of  the 
general  belief  that  citrous  trees  are  shallow-rooted. 
Before  a  rational  irrigation  practice  is  firmly  established, 
farmers  must  become  convinced  that  there  is  no  harm 
whatever  in  cultivating  deeply  and  as  soon  as  possible 
after  each  irrigation. 

40.  Frequency  of  cultivation. — Few  experiments  have 
been  conducted  on  this  subject,  but  the  principles  already 
laid  down  give  a  fairly  clear  indication  of  the  cultivations 
a  field  should  receive  throughout  the  season.  Even  after 
a  thorough  cultivation,  most  soils  gradually  settle  into  a 
more  compact  mass.  In  some  soils  this  settling  is  so  great 


SAVING  WATER  BY  CULTIVATION  59 

that  it  re-establishes  capillary  connections  between  the 
mulch  and  the  moist  soil  below,  and  evaporation  is  then 
resumed.  Such  soils,  which  are  soon  recognized,  should 
be  cultivated  several  times  between  each  irrigation.  When 
soils  show  no  such  tendency  to  settle,  it  may  be  sufficient 
to  give  them  one  good  cultivation  after  each  irrigation. 
Generally,  it  is  well  to  cultivate  the  soil  at  least  once 
every  three  weeks  throughout  the  irrigating  season  and  a 
bi-weekly  cultivation  is  probably  better. 

Summer  showers  also  determine  the  frequency  of 
irrigation.  A  summer  shower,  unless  it  is  very  light, 
beats  down  the  the  mulch  and  usually  saturates  the  soil 
sufficiently  to  establish  vigorous  capillary  communica- 
tion with  the  lower  soil  layers.  This  condition  may  lead 
in  a  few  hours  to  large  evaporation  losses.  For  that 
reason,  every  summer  shower  should  be  followed,  as  soon 
as  the  soil  is  dry  enough,  with  a  thorough  cultivation. 
Where  the  precipitation  comes  chiefly  in  the  fall,  winter 
or  spring,  the  summers  are  relatively  dry  and  the  few 
light  summer  showers  may  easily  be  followed  by  the 
cultivator;  but,  where  the  winter  is  relatively  dry  and  the 
precipitation  comes  chiefly  in  early  or  midsummer,  the 
rains  are  often  so  frequent  and  heavy  that  to  follow  them 
with  cultivators  is  difficult,  if  not  practically  impossible. 
True,  under  such  conditions,  the  water  necessary  in  irri- 
gation is  relatively  smaller,  so  that  evaporation  losses 
can  better  be  sustained  there  than  in  districts  of  dry 
summers,  where  the  annual  precipitation  is  also  usually 
low.  Wherever  possible,  however,  cultivation  should 
follow  both  summer  shower  or  rain  and  irrigation. 

41.  Cultivation  and  soil  fertility. — So  much  has  been 
said  concerning  the  value  of  cultivation  in  the  conserva- 
tion of  soil  moisture  that  one  may  be  led  to  believe  that 


60  IRRIGATION  PRACTICE 

the  whole  virtue  of  cultivation  lies  therein.  However,  cul- 
tivation has  other  beneficial  effects  quite  as  important  as 
the  direct  saving  of  soil  moisture.  The  loosening  of  the 
top  soil  permits  the  entrance  of  the  atmosphere,  with 
the  free  exchange  of  gases  between  the  atmosphere  and 
the  soil  air,  which  ventilates  the  soil  and  enables  various 
physical,  chemical  and  biological  changes  to  take  place. 
The  result  is  of  the  highest  importance  to  plant  life.  The 
condition  of  the  top  soil,  the  part  turned  by  the  plow  and 
stirred  by  the  cultivator,  is  of  first  importance  in  all 
agriculture.  A  striking  illustration  of  this  other  value 
of  cultivation  was  secured  in  the  Utah  work.  In  a  series 
of  tests  designed  to  show  the  moisture-saving  possibili- 
ties of  cultivation,  a  very  careful  account  was  kept  of  the 
total  yield  of  dry  matter  produced  under  the  various  soil 
treatments.  Corn  was  grown  on  four  different  soils  vary- 
ing from  a  coarse  sand  to  a  fine  clay,  and  from  high  fer- 
tility to  great  infertility.  The  following  are  some  of  the 
results  obtained: 

POUNDS  OF  WATER  TRANSPIRED  FOR  ONE  POUND  OF  DRY  MATTER 


Not  cultivated 

Cultivated 

Infertile  sand           

454 

732 

Fertile  sandy  loam      

603 

252 

Fertile  clayey  loam     

535 

428 

Infertile  clay 

753 

582 

In  every  case,  excepting  the  abnormal  infertile  sand, 
the  careful  stirring  of  the  soil  enabled  the  plant  to  pro- 
duce one  pound  of  dry  matter  with  a  smaller  quantity 
of  water  than  when  the  soil  was  not  cultivated.  The 
sandy  loam  was  of  a  self-mulching  nature,  and  really 
lost  water  by  cultivation,  yet  on  this  soil,  also,  cultiva- 


62  IRRIGATION  PRACTICE 

tion  enabled  the  plant  to  produce  dry  matter  at  a  smaller 
water  cost. 

Cultivation  of  the  soil,  therefore,  prevents  the  waste 
of  water  by  evaporation,  and  induces  soil  changes  that 
enable  the  crops  to  produce  larger  yields  with  a  given 
quantity  of  water.  In  truth,  cultivation  may  take  the 
place  of  irrigation. 

42.  Rolling. — Rolling  is  the  opposite  of  cultivation. 
It  compacts  the  top  soil.  As  a  result,  excellent  capillary 
connections  are  established  between  the  top  and  the  sub- 
soil and  water  is  enabled  to  move  upward,  rapidly,  from 
the  lower  layers  to  the  surface,  there  to  be  evaporated 
into  the  air.  There  is  no  more  dangerous  practice  than 
this,  if  evaporation  of  soil  moisture  is  to  be  prevented. 
Moreover,  a  soil  which  has  been  compacted  by  rolling 
offers  much  resistance  to  the  entrance  and  downward 
movement  of  water.  Rolling,  therefore,  (1)  prevents  the 
water  from  entering  the  soil  easily,  and  (2)  allows  the 
water  which  does  enter  the  soil  to  evaporate  rapidly. 
From  the  point  of  view  of  water-conservation  it  is  an 
extremely  wasteful  process. 

In  a  few  special  cases  rolling  may  be  permitted  in  a 
good  system  of  irrigation  agriculture.  For  instance,  in 
raising  sugar  beets  for  factories,  the  soil  is  carefully  rolled 
after  the  planting  of  the  seed,  chiefly  to  insure  good 
germination.  This,  however,  is  not  necessary  except  in 
districts  where  the  spring  precipitation  is  light  or  where 
the  soils  have  been  so  handled  as  to  be  too  dry  for  satis- 
factory germination.  By  proper  methods  of  fall  plowing 
this  precaution  would  probably  be  unnecessary. 

A  special  phase  of  rolling  may  be  of  importance. 
Campbell  recommends  highly  a  sub-surface  packer, 
designed  to  pack  the  soil  at  the  bottom  of  the  plow  fur- 


SAVING  WATER  BY  CULTIVATION  63 

row  while  it  leaves  the  top  soil  loose  and  open.  The  merit 
in  this  process  is  that  the  loose  top  soil  permits  the  easy 
entrance  of  water  into  the  soil  and  also  acts  as  a  mulch 
to  prevent  evaporation.  To  accomplish  such  sub-sur- 
face packing  the  Campbell  machine  may  be  used,  or  the 
soil  may  be  thoroughly  cross-disked. 

Rolling,  whether  on  top  or  below  the  surface,  is  of 
small  and  questionable  value  in  any  system  of  irriga- 
tion practice. 

REFERENCES 

BRIGGS,  LYMAN  J.,  and  BELZ,  J.  O.    Dry-Farming  in  Relation  to 

Rainfall  and   Evaporation.    United   States   Bureau   of   Plant 

Industry,  Bulletin  No.  188  (1911). 
BUCKINGHAM,   EDGAR.     Contributions  to  Our  Knowledge  of  the 

Aeration  of  Soils.     United  States  Bureau  of  Soils,   Bulletin 

No.  25  (1904). 
BUCKINGHAM,  EDGAR.    Studies  on  the  Movement  of  Soil  Moisture 

United  States  Bureau  of  Soils,  Bulletin  No.  38  (1907). 
FORTIER,  SAMUEL.    Evaporation  Losses  in  Irrigation  and  Water 

Requirements  of  Crops.    United  States  Office  of  Experiment 

Stations,  Bulletin  No.  177  (1907). 
FORTIER,  SAMUEL,  and  BECKETT,  S.  H.  Evaporation  from  Irrigated 

Soils.    United  States  Office  of  Experiment  Stations,  Bulletin 

No.  248  (1912). 
WHITNEY,  MILTON,  and  CAMERON,  F.  K.    Investigations  in  Soil 

Fertility.  United  States  Bureau  of  Soils,  Bulletin  No.  23  (1904). 
WIDTSOE,  J.  A.    Factors  Influencing  Evaporation  and  Transpira- 
tion.  Utah  Experiment  Station,  Bulletin  No.  105  (1909). 
WIDTSOE,  J.  A.,  and  MCLAUGHLIN,  W.  W.  The  Movement  of  Water 

in  Irrigated  Soils.    Utah  Experiment  Station,  Bulletin  No.  115 

(1912). 
WIDTSOE,  J.  A.  Dry-Farming.  Chapter  VIII  (1911). 


CHAPTER  V 

SOIL  CHANGES  DUE  TO  IRRIGATION  WATER 

THE  soil  cannot,  directly,  be  greatly  changed  by  the 
farmer.  As  it  is,  so,  in  a  large  measure,  it  must  remain. 
Tillage  implements  modify  only  slightly  the  upper  layer 
of  the  soil.  Water,  however,  may  cause  fairly  large 
changes  in  the  soil  to  the  full  depth  to  which  it  pene- 
trates. Irrigation,  therefore,  with  its  power  of  regula- 
ting the  quantity  of  water  applied,  may  be  made  a  means 
of  modifying  soil  properties.  Physical,  chemical  and 
biological  soil  changes  are  induced  by  irrigation,  and 
some  of  the  most  important  principles  of  a  permanent 
system  of  irrigation  agriculture,  depend  upon  the  effects 
of  water  upon  soil. 

43.  Contraction  and  moisture  film. — If  a  camePs-hair 
brush  be  dipped  in  water,  and  then  removed,  the  hairs 
cling  together  to  form  a  narrow  and  rather  hard  brush 
suitable  for  use  in  painting.  If  a  trifle  of  the  water  in  the 
brush  be  squeezed  out,  the  brush  becomes  rather  stiffer 
than  it  was  before,  but  if  more  water  be  removed,  the 
brush  become  looser  and  looser  until  it  is  dry  and  fluffy. 
This  adhesion  of  the  hairs  is  due  (1)  to  the  contraction 
of  the  films  surrounding  each  little  hair,  and  (2)  to  the 
contraction  of  the  water  film  enveloping  the  whole  brush. 
(Fig.  15.) 

In  like  manner,  the  particles  of  a  soil,  when  wetted  or 
dried,  tend  to  move  either  more  closely  together  or  farther 
apart,  and  the  soil  becomes  more  or  less  rigid.  When 

(64) 


SOIL  CHANGES  DUE  TO  IRRIGATION  65 

water  is  applied  to  a  soil  it  forms  a  film  around  each  of 
the  particles  of  widely  differing  sizes;  and  further,  many 
small  and  large  particles  may  form  a  larger  composite 
particle  or  crumb  with  one  continuous  film  surrounding 
it.  The  soil  should  possess  a  well-devel- 
oped crumb  structure;  for  the  plant  has 
then  a  better  chance  to  develop  than  if 
the  individual  particles  remain  separate 
in  single-grain  structure. 

44.  Cohesion  of  soil  particles. — By 
direct  examination,  every  good  farmer 
may  determine  whether  the  soil  is  in 
proper  condition  for  plowing  or  for  other 
cultural  operations.  Usually  this  condi- 
tion means  that  the  proportion  of  mois- 
ture in  the  soil  is  such  that  a  plow  or  a 
cultivator  may  be  passed  through  it  with 
the  least  resistance  and  without  destroy- 
ing the  crumb  structure  or  tilth.  The 
question  of  the  force  with  which  dry  or 
moist  soil  particles  stick  to  each  other  is 
not  of  itself  of  very  great  importance;  FIG.  15.  Adhesion  of 
but  it  is  of  interest  in  showing  the  effect  hairs  due  to  water* 
of  various  proportions  of  water  on  the  properties  of  the 
different  soils.  Pure  clay  dries  to  a  very  hard  mass, 
difficult  to  break.  If  to  the  clay  be  added  sand,  humus, 
gypsum  or  lime,  the  resulting  mass,  when  dry,  may  be 
broken  with  less  than  one-fifteenth  the  force  necessary 
to  break  the  pure  clay.  In  fact,  coarse  sands  or  soils  rich 
in  gypsum  or  lime,  as  they  dry,  often  fall  apart  into  a 
coarse  mass,  which  forms  a  natural  mulch  over  the  soil. 

The  force  with  which  soil  particles  are  held  together 
depends,  primarily,  upon  three  factors:  (1)  the  physical 


66  IRRIGATION  PRACTICE 

constitution  of  the  soil;  (2)  the  water  content,  and  (3) 
the  presence  of  various  salts.  The  finer  the  soil  is,  the 
more  firmly  the  dry  particles  are  held  together.  As  the 
soil  water  increases,  clay  is  less  firmly,  and  sand  more 
firmly,  held  together.  The  presence  of  soluble  salts 
tends,  in  general,  to  reduce  the  force  with  which  soil  par- 
ticles stick  together,  though  lime  and  other  substances 
have  the  opposite  effect. 

Of  chief  importance  to  the  irrigation  farmer  is  the 
knowledge  of  how  varying  amounts  of  water  affect  the 
cohesion  of  soil  particles,  since  it  is  within  his  power  to 
regulate  the  quantity  of  water  in  the  soil.  Cameron  and 
Gallagher  have  done  some  excellent  work  on  this  subject. 
They  concerned  themselves  only  with  the  percentages  of 
soil  water  which  are  found  in  actual  agricultural  practice; 
for,  large  additions  of  water,  beyond  the  saturation  point 
of  the  soil,  always  cause  the  soil  crumbs  to  fall  apart  into 
their  constituent  particles;  and,  likewise,  at  moisture 
contents  below  the  wilting  point,  the  cohesive  powers  of 
the  soil  grains  have  little  agricultural  meaning. 

Sand,  loam,  clay  and  humus  soils  were  studied.  In 
all  of  these,  save  the  clay,  as  the  soil  moisture  increased, 
the  force  with  which  the  soil  crumbs  were  held  together 
at  first  decreased  up  to  a  definite  point,  then  increased, 
and,  by  the  addition  of  more  water,  decreased  again  to 
the  point  of  minimum  cohesion.  In  other  words,  as  water 
is  added  to  a  dry  soil,  the  soil  first  gradually  softens;  then 
gradually  hardens;  then  rapidly  softens  until  it  is  a  mushy 
mass.  The  point  of  low  cohesion,  or  easy  penetration  at 
which  tillage  implements  may  be  passed  through  the  soil 
with  small  resistance,  corresponded,  generally,  with  the 
so-called  point  of  optimum  water  content  in  the  soil; 
that  is,  the  degree  of  wetness  at  which,  according  to  the 


SOIL  CHANGES  DUE  TO  IRRIGATION  67 

judgment  of  experienced  tillers  of  the  soil,  the  soil  is  in 
the  best  condition  for  plant-growth.  In  the  case  of  the 
clay  soil,  as  more  water  was  applied,  the  force  of  cohesion 
continued  steadily  to  diminish,  with  no  definite  point  at 
which  a  temporary  hardening  occurred.  At  a  definite 
degree  of  wetness,  however,  the  clay  soil  is  in  the  best 
condition  for  working  and  for  plant-growth.  This  is  in 
full  harmony  with  the  known  properties  of  clay. 

The  point  of  optimum  water  content  is,  approxi- 
mately, identical  with  the  field  water  capacity  discussed 
in  Chapter  II.  It  seems  clear  that,  when  the  soil  contains 
a  medium  amount  of  water,  that  is,  a  quantity  lying 
between  the  maximum  water  capacity  and  the  point  of 
lento-capillarity,  it  can  be  most  easily  worked,  and  is  in 
best  condition  for  plants.  It  is  interesting  to  note  how  this 
intermediate  point  continually  appears  in  the  study  of 
the  relation  of  soils  and  plants  to  varying  water  content. 

45.  Volume  changes  of  soils. — It  follows  that,  if  such 
differences  in  the  force  with  which  the  soil  crumbs  are 
held  together  are  induced  by  the  application  of  varying 
quantities  of  water,  the  soil  particles  themselves  must 
actually  move  and  rearrange  themselves,  as  water  is 
added  to  or  removed  from  the  soil.  Such  movements  of 
the  soil  particles  would  naturally  cause,  also,  correspond- 
ing changes  in  the  volume  of  the  soil.  This  is  an  estab- 
lished fact,  well  known  to  every  practical  farmer.  If 
wet  clay  is  allowed  to  dry  it  shrinks,  with  the  formation 
of  large  cracks  in  the  ground.  When  water  is  again  added, 
the  clay  swells  and  the  cracks  largely  disappear.  In  a 
large  measure,  this  is  true  of  all  agricultural  soils.  As  they 
receive  water,  they  swell;  as  they  dry,  they  contract. 

The  changes  in  the  soil  volume,  due  to  the  addition 
of  water,  are  very  great.  In  clay  and  humus  soils  they 


68 


IRRIGATION  PRACTICE 


are  often  as  high  as  50  to  75  per  cent  of  the  original 
volume;  with  average  soils,  receiving  moderate  quanti- 
ties of  water  within  the  limits  of  practical  agriculture, 
the  volume  changes  are  from  7  to  12  per  cent  of  the 
original  volume.  Such  fairly  large  variations,  occurring 
over  acres  of  land,  represent  great  total  changes,  capable 
of  modifying  deeply  the  character  of  the  soil. 

The  reason  for  such  volume  changes  is  simple.  In  a 
dry  soil  the  particles,  lying  rather  closely  side  by  side, 
occupy  a  relatively  small  space.  When  water  is  added, 
the  soil  particles  group  themselves  into  larger  loose  aggre- 
gates or  crumbs,  which  occupy  more  space.  There  is  a 


FIG.  16.  Cracked  river  sediments  showing  volume  changes  due  to  water. 

continuous  arrangement  and  rearrangement  of  soil  parti- 
cles, and  a  corresponding  variation  in  the  soil  volume  as 
the  percentage  of  water  in  the  soil  changes. 

Cameron  and  Gallagher  found  that,  as  water  is  added 
to  the  soil,  the  volume  becomes  larger  and  larger,  until  a 
certain  definite  point  is  reached,  after  which  the  volume 


SOIL  CHANGES  DUE  TO  IRRIGATION  69 

becomes  smaller  and  smaller.  This  point  of  largest  vol- 
ume coincides  almost  exactly  with  the  point  at  which  the 
penetration  of  the  soil  is  easy;  which,  as  has  been  said, 
is  the  point  of  optimum  water  content.  The  farmer  who 
desires  to  keep  the  soil  in  the  best  tilth,  from  top  to  lower 
depths,  in  order  to  increase  the  air  space  in  the  soil  and 
to  permit  the  easy  penetration  of  roots,  can  do  so  by  main- 
taining in  the  soil  a  moderate  quantity  of  water,  between 
the  point  of  lento-capillarity  and  maximum  capacity, 
somewhere  in  the  neighborhood  of  the  field  capacity. 
The  farmer  who  depends  upon  the  rainfall  and,  therefore, 
cannot  control  his  water  supply,  cannot  well  maintain 
the  soil  in  this  good  condition.  The  irrigation  farmer,  on 
the  other  hand,  who  may,  usually,  apply  water  at  will, 
can  so  plan  his  irrigation,  when  he  knows  his  soil,  as  to 
maintain  the  land  during  the  larger  part  of  the  season 
in  the  most  desirable  condition  for  plant-growth.  (Fig.  16.) 

46.  Effect  on  top  soil. — Through  the  top  soil,  whether 
under  irrigation  or  rainfall,  all  water  added  to  a  soil 
ordinarily  passes.  The  top  soil  first  becomes  completely 
saturated,  then  it  dries  out  quite  thoroughly,  and  the 
process  is  frequently  repeated.  It  follows,  therefore,  that 
the  top  soil  is  subject,  almost  from  day  to  day,  to  the 
greatest  changes,  physical,  chemical  and  bacteriological. 
In  the  greater  depths,  more  water  is  held  over  from  irri- 
gation to  irrigation,  and  consequently  the  changes  due 
to  varying  moisture  content  do  not  go  on  to  the  same 
degree.  It  is  interesting  to  note  that,  in  a  soil  properly 
irrigated,  the  lower  layers  of  soil  to  the  depth  of  10  to  12 
feet  are  kept,  from  irrigation  to  irrigation,  within  1  to  4 
per  cent  of  the  point  at  which  the  structure  of  the  soil 
is  the  most  desirable. 

It  is  a  common  observation  that  irrigation  tends  to 


70  IRRIGATION  PRACTICE 

pack  the  top  soil,  and  that  cultivation  must  be  performed 
after  each  irrigation,  if  the  top  soil  is  to  be  kept  in  a  thor- 
oughly loose  condition.  This  is  probably  due,  chiefly,  to 
the  excessive  wetting  after  each  irrigation,  which  breaks 
down  the  soil  crumbs  into  a  single-grain  structure.  The 
effect  of  the  successive  thorough  wetting  and  drying 
characteristic  of  irrigation  is  of  interest  to  the  farmer. 

47.  Successive    wetting   and    drying. — When    irriga- 
tion water  is  applied,  the  soil  mass  expands,  only  to  con- 
tract gradually  as  the  water  is  lost  by  evaporation  or 
transpiration.   The  effect  of  this  successive  expansion  and 
contraction    was    also    investigated    by    Cameron    and 
Gallagher,  with  rather  definite  results.    At  the  first  irri- 
gation the  soil  expands,  and  then  contracts  to  a  certain 
definite  degree;  at  the  second  irrigation  the  soil  does  not 
expand  quite  so  much,  but  contracts  a  little  more  than  at 
the  first  irrigation;  at  the  third  irrigation  the  expansion 
is  yet  smaller  and  the  contraction  proportionally  larger; 
at  each  successive  irrigation,  the  soil  becomes  more  and 
more  compacted,  until  a  condition  of  natural  packing  is 
reached   at  which   the    expansion  and    the   contraction, 
after  each  irrigation,  are  so  nearly  the  same  as  to  result 
in  no  practical  volume  change.    If  too  much  or  too  little 
water  is  applied  at  each  irrigation,  so  that  the  soil  is  per- 
manently kept  too  dry  or  too  wet,  the  condition  of  natural 
packing  is  prevented. 

48.  Natural  packing  of  soil. — The  condition  of  natural 
packing  is,  however,  far  from  being  the  closest  possible 
packing;  it  is  rather  the  packing  of  highest  advantage 
to   plant-growth.     If   the   soil   has   become   too   tightly 
packed,  then  the  expansions  and  contractions  of  succes- 
sive irrigations  will  tend  to  loosen  the  soil,  until  the  con- 
dition of  natural  packing  is  reached;  if  the  soil  has  become 


SOIL  CHANGES  DUE  TO  IRRIGATION  71 

too  loose,  it  will  be  brought  to  the  condition  of  natural 
packing  by  excessive  irrigations.  A  soil  properly  irrigated, 
that  is,  one  which  contains,  after  each  irrigation,  the 
optimum  percentage  of  water  (approximately  with  the 
field  water  capacity  saturated)  will,  in  time,  under  this 
law  of  natural  packing  by  successive  irrigations,  acquire 
a  structure  best  fitted,  considering  the  nature  of  the  soil, 
for  the  support  of  plant-life.  The  top  soil,  only,  which  is 
over-saturated  at  each  irrigation,  and  thoroughly  dried 
out  at  each  cultivation,  needs  mechanical  means  to  be 
kept  in  the  best  structural  condition. 

When  the  soil  is  in  the  condition  of  natural  packing, 
the  soil-water  film  is  continuous,  and  water  can  move 
through  it  rather  freely  from  soil  crumb  to  soil  crumb. 
From  the  surface  of  such  a  soil,  if  allowed  to  remain 
uncultivated,  the  water  stored  in  the  lower  depths  may 
readily  escape  by  evaporation  from  the  top.  Under  irri- 
gated conditions,  where  water  economy  is  paramount, 
the  top  soil  must  be  kept  much  looser  than  in  the  con- 
dition of  natural  packing.  For  that  reason,  as  was 
emphasized  in  the  preceding  chapter,  it  is  necessary  to 
follow  every  irrigation  with  a  thorough  cultivation,  so 
that  the  top  soil  may  always  be  a  dry,  loose  mulch  to 
prevent  evaporation. 

49.  Soil  temperature. — The  temperature  of  the  soil 
is  often  of  very  high  importance,  especially  in  the  spring 
at  the  time  of  germination  and  early  growth.  It  is  of 
importance,  also,  at  all  ages  of  plant-growth.  Patten 
has  made  elaborate  investigations  to  determine  the 
quantity  of  water  that  will  permit  the  most  ready  trans- 
mission of  heat  in  the  soil.  He  found  that  a  medium 
quantity  of  water,  not  far  removed  from  that  which 
corresponds  to  the  j)oint  of  easy  penetration  and  largest 


72  IRRIGATION  PRACTICE 

volume — the  point  of  optimum  water  content  as  dis- 
cussed— is  the  point  at  which  heat  moves  most  readily 
through  the  soil.  The  growing  season  in  the  irrigated 
region  is  usually  very  warm,  and  it  might  be  of  considera- 
ble importance  in  hastening  maturity,  or  in  aiding  plant- 
growth,  to  enable  the  soil  to  absorb  much  heat  and  to 
conduct  it  readily  into  the  lower  layers,  where  the  plant 
roots  are  working. 

This  is  of  special  importance  in  districts  where  the 
irrigation  water  is  taken  from  the  cold  mountain  streams 
that  are  often  only  a  few  degrees  above  the  freezing  point. 
Under  such  conditions,  the  ready  absorption  and  con- 
duction of  heat  by  the  soil  may  determine  the  rate  of 
growth  and  length  of  the  growing  season,  both  of  which 
are  often  of  vital  importance.  All  in  all,  our  knowledge 
of  the  relation  of  water  to  the  physical  properties  of  soils 
would  indicate  that  the  wise  irrigation  farmer  will  apply 
to  the  soil  only  moderate  quantities  o£  water.  Too  little 
or  too  much  water  at  a  time  are  equally  dangerous,  and 
threaten  loss  to  the  farmer. 

50.  Water  a  universal  solvent. — Practically  every 
known  substance  is  soluble  to  some  degree  in  pure  water. 
The  rocks  and  minerals,  the  fragments  of  which  consti- 
tute soil  are,  therefore,  partly  dissolved  in  the  soil  water. 
Many  of  the  common  minerals  of  chief  occurence  in  soils, 
such  as  apatite,  clay,  mica,  hornblend  and  serpentine, 
dissolve  in  water  to  the  amount  of  4  per  cent  to  1  per 
cent  of  their  total  weight.  The  solvent  power  of  water 
depends  on  a  number  of  conditions,  the  most  important 
of  which  under  field  conditions  are  (1)  temperature,  (2) 
dissolved  carbon  dioxide,  (3)  dissolved  inorganic  salts,  (4) 
dissolved  organic  compounds,  and  (5)  living  organisms. 

The  higher  the  temperature,  the  more  rapidly  does 


SOIL  CHANGES  DUE  TO  IRRIGATION  73 

solution  go  on.  In  districts  where  irrigation  is  indispen- 
sable, the  average  temperature  during  the  growing  season 
is  generally  high,  and  the  solution  of  soil  in  the  applied 
water  goes  on  rapidly.  In  many  places  the  irrigation 
water  itself,  taken  from  comparatively  large  rivers,  is 
very  warm,  which,  added  to  the  high  average  daily  tem- 
perature, accelerates  greatly  the  rate  of  solution.  In 
otiher  places,  however,  the  water,  as  it  issues  from  the 
mountain  canyons,  is  almost  immediately  spread  over  the 
soil.  Such  water,  fresh  from  the  melting  snow-banks,  is 
of  low  temperature  and  chills  the  soil  considerably,  and 
in  all  probability  retards  the  rate  of  solution  of  the  soils. 

In  practically  all  natural  waters  there  is  an  abundance 
of  the  gas  carbon  dioxid  obtained  by  the  water  from 
decaying  organic  remains  in  the  soils  through  which  it 
passes.  Such  carbonated  waters  exert  a  strongly  solvent 
action  upon  the  minerals  of  the  soil ;  indeed,  carbon  dioxid 
is  by  far  the  most  important  of  the  factors  that  influence 
the  solubility  of  the  soil  in  water.  Natural  waters  gen- 
erally contain  also  a  large  proportion  of  inorganic  salts 
which,  as  a  rule,  increase  the  solvent  action  of  water. 
Likewise,  solutions  of  the  organic  substances  formed  from 
the  decomposition  of  plant  and  animal  residues  exert  a 
strongly  solvent  effect  on  soils.  Finally,  the  presence  of 
living  organisms  in  irrigation  water  or  in  soil  have  much 
to  do  with  the  rate  at  which  the  soil  constituents  are 
dissolved. 

51.  Humid  and  arid  soils  contrasted. — The  solvent 
power  of  water  modifies  so  deeply  the  composition  and 
properties  of  soil  that  it  is  one  of  the  most  important 
factors  in  the  establishment  of  a  rational  system  of  irri- 
gation practice.  The  soil-making  forces,  from  the  begin- 
ning, have  tended  to  make  soils  more  soluble,  that  is,  to 


74  IRRIGATION  PRACTICE 

make  their  constitutents  more  easily  available  to  plants. 
Under  humid  conditions,  with  a  high  annual  rainfall, 
the  soluble  soil  constituents  thus  formed  have  been 
largely  washed  out  of  the  soil  into  the  country  drainage 
and  finally  into  the  ocean.  In  arid  districts,  with  a 
scanty  rainfall  and  less  ample  drainage,  most  of  the  soluble 
soil  constituents  remain  in  the  soil.  Humid  soils,  there- 
fore, contain  little  soluble  matter;  arid  soils,  relatively 
much.  This  is  one  of  the  chief  differences  between  the 
two  classes  of  soils.  Normal  arid  soils  do  not,  however, 
contain  large  proportions  of  soluble  matter.  In  an  investi- 
gation of  a  great  variety  of  fertile  Utah  soils,  50  grams  of 
soil  were  shaken  with  500  cc.  of  distilled  water  for  twenty- 
four  hours.  The  soluble  matter  thus  extracted  varied 
from  .2  per  cent  to  .48  per  cent.  Under  more  abnormal 
conditions,  as  will  be  explained  in  the  chapter  on  alkali, 
soluble  matter  may  be  present  to  the  extent  of  several 
per  cent,  and  then  the  soil  must  be  subjected  to  special 
treatment  before  it  can  serve  the  farmer. 

52.  Continuous  solubility  of  soils. — It  is  practically 
impossible  to  wash  the  soil  so  thoroughly  as  to  remove 
from  it  all  substances  capable  of  going  into  solution. 
Many  experiments  have  been  made  on  this  subject,  all 
with  fairly  concordant  results.  For  example,  Schultze 
treated  a  given  weight  of  soil  with  a  definite  quantity  of 
water  for  six  days,  after  which  the  solution  was  filtered 
off  and  analyzed.  This  was  repeated  every  six  days  dur- 
ing six  periods.  During  the  first  treatment,  1,000,000  parts 
of  solution  contained  535  parts  of  mineral  matter  dis- 
solved from  the  soil;  during  the  second,  120;  then  261,  203, 
260,  and  200  parts  during  the  sixth  period.  That  is, 
while  the  first  treatment  dissolved  most,  every  successive 
treatment  dissolved  considerable  quantities  of  soil  con- 


SOIL  CHANGES  DUE  TO  IRRIGATION  75 

constituents,  and  more  went  into  solution  during  the 
sixth  than  during  the  second  period.  In  all  probability, 
if  these  successive  washings  had  been  continued,  they 
would  have  resulted  in  the  continuous  removal  of  appre- 
ciable quantities  of  valuable  soil  constituents.  The  con- 
tinuous solubility  of  soils  has  a  very  important  bearing 
upon  the  permanent  production  of  crops  on  any  one  soil. 


FIG.  17.  Midsummer  snow  in  the  tops  of  the  mountains.    The  source  of  irrigation 
water.   This  water  is  very  pure. 


76  IRRIGATION  PRACTICE 

King  found  that  eleven  successive  extractions  of  soil  with 
water  removed  more  than  eleven  times  the  quantity  of 
some  constituents  that  was  extracted  the  first  time.  The 
continuous  solubility  of  soils  is  well  established,  and  it  has, 
no  doubt,  an  important  bearing  on  the  permanent  pro- 
duction of  crops. 

Whenever,  therefore,  irrigation  water  is  applied  to 
the  soil,  a  part  of  the  soil  is  dissolved,  providing  that  the 
substances  dissolved  by  the  previous  irrigation  have  been 
somewhat  thoroughly  removed  by  plant  roots  or  by 
drainage.  Naturally,  not  all  soil  constituents  are  extracted 
at  the  same  rate  by  successive  applications  of  water. 
Approximately  the  same  quantity  of  potash  goes  into 
solution  from  extraction  to  extraction,  while  a  very  large 
part  of  the  nitrates  is  extracted  during  the  first  applica- 
tion of  water,  leaving  little  for  the  later  ones;  unless, 
indeed,  during  the  interval  between  irrigations,  nitrates 
have  been  added  or  cultural  treatments  have  permitted 
a  very  rapid  rate  of  nitrification. 

53.  Absorption  by  soils. — The  solution  of  soil  con- 
stituents occurs  most  readily  at  the  surfaces  of  the  soil 
grains.  The  dissolved  substances,  under  the  influence 
of  somewhat  obscure  manifestations  of  the  laws  of  attrac- 
tion, are  held  in  high  concentration  very  near  the  sur- 
faces, and  the  outward  movement  through  the  water- 
film  of  the  dissolved  materials  is  very  slow.  This  property 
of  firmly  holding  certain  soluble  substances  near  the  sur- 
faces of  the  soil  particles,  known  as  absorption,  is  of  tremen- 
dous importance  in  conserving  the  fertility  of  agricultural 
soils,  whether  under  humid  or  arid  conditions.  The  first 
water  added  to  a  soil,  as  has  already  been  explained,  is 
held  as  thin  films  around  the  soil  grains.  Drainage  through 
the  soil  occurs  only  after  these  films  have  acquired  a  cer- 


SOIL  CHANGES  DUE  TO  IRRIGATION 


77 


tain  definite  thickness.  Water  added  beyond  this  point 
fills  the  capillary  tubes  and  under  the  influence  of  gravity 
moves  downward  into  the  country  drainage.  As  this 
gravitational  water  moves  downward,  the  soil-water  film 
clinging  closely  around  the  soil  grains  is  not  materially 
affected.  A  small  part  of  the  outer  film  may  be  carried 
downward,  but  the  inner  part,  near  the  surfaces  of  the 
soil  grains,  where  the  dissolved  soil  constituents  are  held 
in  greatest  concentration,  probably  does  not  move  at  all 
with  the  gravitational  water.  Enough  is  carried  along, 
however,  to  affect  materially  the  composition  of  the  drain- 
age water.  In  one  of  the  Utah  experiments,  water  was 
applied  to  a  very  loose  gravelly  soil,  scarcely  2  feet  deep, 
and  underlaid  with  a  cobble  rock  formation  of  unknown 
depth.  Underground  collecting  chambers  were  con- 
structed to  collect  the  drainage  water.  So  gravelly  was 
the  land  that  within  half  an  hour  after  water  had  been 
applied,  it  drained  through  into  the  lysimeters.  As  an 
average  of  one  season's  test,  the  following  results  were 
obtained : 


Parts  per  million 

As  applied 

As  drained 

Total  solids 

162 
75 

58 
23 
1.4 
0 
Trace 

242 
106 
64 
30 
10.5 
1.4 
5.1 

Volatile  matter        

Lime     

Magnesia      

Potash 

Phosphoric  acid       .        . 

Nitric  acid    

It  will  be  noted  from  these  figures  that,  even  under 
conditions  of  easy  and  rapid  drainage,  much  valuable 
material  is  washed  out  of  the  soil.  Nevertheless,  as  will 
be  shown,  the  parts  of  total  solids  in  1,000,000  parts  of 


78  IRRIGATION  PRACTICE 


the  drainage  water  were  not  much  higher  than  in  many  of 
the  streams  and  rivers  used  for  irrigation.  The  lime  and 
magnesia  were  not  washed  out  to  any  great  extent,  but 
the  potash,  phosphoric  acid  and  nitric  acid,  the  three 
most  important  constituents  of  the  soil,  were  propor- 
tionally much  more  abundant  in  the  drainage  water  than 
in  the  original  irrigation  water.  Analyses  of  drainage 
waters  in  various  countries  lead  to  similar  results.  Hil- 
gard,  in  a  collection  of  analyses  of  drainage  water  from 
European  countries,  has  shown  that  the  parts  of  total 
solids  in  1,000,000  parts  of  water  range  from  140  to  721, 
with  an  average  of  352.6,  which  is  somewhat  higher  than 
the  242  found  in  the  above  Utah  experiment. 

54.  Composition  of  drainage  water. — It  may  be  said 
safely  that  the  concentration  of  drainage  water  under 
normal  conditions  is  not  extraordinarily  high,  but  hovers 
in  the  neighborhood  of  200  to  400  parts  of  total  solids 
in  1,000,000  parts  of  water.  Under  abnormal  conditions, 
these  figures  may  be  much  larger.  If,  for  instance,  the 
soil  is  rich  in  organic  matter,  as  after  heavy  manuring, 
the  drainage  water  may  show  a  high  proportion  of  organic 
matter;  if  the  soil  is  of  an  alkali  nature,  the  drainage 
water  frequently  contains  tremendously  large  quantities 
of  soluble  matter.  In  one  of  the  reclamation  experiments 
of  the  United  States  Bureau  of  Soils  at  Billings,  Mon- 
tana, the  drainage  water  from  an  alkali  tract,  which  had 
been  under  drained  for  the  purpose  of  removing  the  alkali, 
contained  from  250  to  9,000  parts  of  dissolved  matter  in 
1,000,000  parts  of  water;  in  the  drainage  water  from  a 
similar  tract  located  near  Salt  Lake  City,  were  found 
10,710  to  20,346  parts  of  dissolved  matter  in  1,000,000 
parts  of  water.  These  are  extraordinary  concentrations 
of  drainage  water  which  occur  only  when  the  soils  are 


SOIL  CHANGES  DUE  TO  IRRIGATION  79 

abnormally  rich  in  soluble  constituents.  Normal  soils,  by 
the  power  of  absorption,  retain  most  of  the  soluble  mate- 
rials, so  that  the  concentration  of  the  drainage  water  is 
kept  low,  as  above  given. 

55.  Concentration  of  soil  moisture. — Results  of  strik- 
ing interest  are  obtained  when  the  possible  concentra- 
tions of  soil  water  are  calculated.    If  it  be1  assumed  that 
a  soil  with  .1  per  cent  of  soluble  matter  under  ordinary 
laboratory  methods  contains  an  average  of  20  per  cent  of 
moisture  to  a  depth  of  10  feet,  which  is  the  approximate 
condition  of  an  irrigated  clay  loam  immediately  after  a 
5-inch  irrigation,  and  if  all  the  soluble  matter  goes  into 
solution  in  the  water  thus  added,  the  soil  solution  will  have 
a  concentration  of  about  5,000  parts  of  dissolved  matter 
for  every  1,000,000  parts  of  water.   This  is  far  in  excess  of 
the  composition  of  any  drainage  water  from  such  soils 
under  normal  field  conditions.     Moreover,  as  evapora- 
tion goes  on,  this  concentration  must  increase  consider- 
ably.   Arid  soils  usually  contain  more  than  .1  per  cent  of 
soluble  matter;  if  .5  per  cent  is  held  by  the  soil,  for  instance, 
the  concentration  under  the  above  assumptions  will  be 
25,000  parts  of  dissolved  substance  for  every  1,000,000 
parts  of  water — a  concentration  larger  than  that  of  the 
drainage  water  from  the  above  mentioned  alkali  reclama- 
tion tract  near  Salt  Lake  City.    Little  is  known,  as  yet, 
about  the  exact  concentration  of  soluble  matter  in  the 
film  held  about  the  soil  grains;  but  it  must  be  compara- 
tively high.    In  such  solutions  the  feeding  roots  of  plants 
are  bathed. 

56.  Loss  by  drainage. — The  repeated  application  of 
water  to  soils,  in  quantities  sufficient  to  drain  through, 
results  disastrously,  because,  even  though  the  quantity  of 
soluble  matter  taken  out  each  time  is  small,  in  the  end  the 


80  IRRIGATION  PRACTICE 

total  is  considerable.  The  evidence  of  this  is  found  in  the 
lean  and  washed-out  soils  of  humid  districts,  where  the 
rainfall  is  large  enough  to  permit  steady  drainage  with- 
out the  counterbalancing  effects  of  a  tropical  warmth. 
In  arid  districts,  likewise,  where  over-irrigation  has  pre- 
vailed, soils  have  been  permanently  injured  by  the  loss 
of  plant-food — carried  off  in  the  drainage. 

The  loss  of  plant-food  is  only  one  of  the  many  injurious 
effects  of  the  excessive  use  of  water.  In  arid  districts  the 
drainage  water,  resulting  from  over-irrigation,  frequently 
accumulates  in  some  lower-lying  closed  basin,  such  as  in 
the  lowest  part  of  a  valley.  At  this  point  the  ground 
water  rises  higher  and  higher  as  excessive  irrigation  is 
practised  on  the  higher  land,  until  the  water-table  is  so 
near  the  surface  that  water  may  be  lifted  from  it  to  the 
surface  by  capillary  attraction.  When  this  condition  has 
been  reached,  continuous  evaporation  from  the  soil  sur- 
face occurs.  The  soluble  matters  contained  by  the  water 
which  is  left  behind  increase,  first,  the  concentration  of 
the  ground  water,  and  secondly,  as  evaporation  goes  on, 
fill  the  upper  layers  of  soil  with  soluble  salts,  often  with 
a  formation  of  an  alkali  crust.  Over-irrigation  thus 
becomes  one  of  the  chief  sources  of  the  dreaded  alkali. 

The  disastrous  results  of  the  excessive  use  of  water 
prevail  over  large  areas  in  almost  every  irrigated  section 
of  the  world.  Leaky  canals  have  permitted  large  quanti- 
ties of  water  to  soak  through  great  areas  of  fertile  soils, 
until,  heavily  charged  with  precious  plant-food,  they  have 
accumulated  in  lower  basins.  Farmers,  anxious  to  pro- 
tect themselves  against  the  drought,  and  believing  that 
the  more  water  used  the  more  certain  would  be  the  crop, 
have  so  over-irrigated  their  lands  as  to  permit  a  more  or 
less  constant  drainage  into  subsoil  and  lower-lying  places. 


SOIL  CHANGES  DUE  TO  IRRIGATION  81 

In  view  of  this  danger,  the  irrigation  farmer  must  so  con- 
trol the  application  of  water  to  the  soil  that  no  more  is 
added  than  is  necessary  to  produce  the  maximum  film 
around  the  soil  grains.  Drainage  must,  as  a  rule,  be 
avoided.  A  knowledge  of  the  depth  and  character  of  the 
soil  and  devices  for  measuring  water  make  this  easily  done. 

57.  Upward  leaching. — In  yet  another  manner  is  the 
nature  of  the  soil  materially  influenced  by  irrigation.  If 
water  is  applied  in  moderation,  and  according  to  the  best 
principles  of  irrigation,  the  soil-water  film  is  simply  thick- 
ened to  a  distance  greater  or  smaller,  according  to  the 
quantity  applied.  The  water  thus  added  is  in  part  lost 
by  evaporation  at  the  top  soil,  and  in  part  is  taken  from 
the  soil  through  the  plant  roots.  While  the  plant  roots 
often  penetrate  the  soil  to  a  depth  of  8  to  10  feet  or  more, 
yet  the  greatest  abundance  of  plant  roots  is  found  in  the 
upper  soil.  Under  heavy  irrigation,  especially,  when 
plants  are  not  obliged  to  drive  their  roots  deeply  in  search 
of  water,  the  greatest  root-development  is  usually  found 
in  the  upper  3  feet  or  so  of  the  soil.  However,  even  these 
surface  roots  draw  water  from  much  greater  depths;  for, 
as  has  already  been  explained,  the  removal  of  water  in  an 
upper  soil  results  in  a  slow  capillary  flow  of  water  from 
below,  to  re-establish  equilibrium.  As  the  water  moves 
upward,  to  replace  that  removed  by  the  roots,  it  carries 
with  it  some  of  the  materials  dissolved  from  the  lower 
soil  layers. 

Under  wise  irrigation,  therefore,  there  is  a  gradual 
movement  of  the  soluble  soil  constituents  toward  the  sur- 
face, where  the  soil  moisture  often  becomes  so  concen- 
trated that  the  salts  crystallize  out  and  form  layers  of 
alkali.  When  irrigation  is  again  applied,  these  soluble 
matters  are  in  part  washed  downward;  but,  owing  to  the 
F 


82  IRRIGATION  PRACTICE 

laws  of  absorption,  they  are  held  very  near  to  the  surfaces 
of  the  soil  grains  and  are  not  easily  dislodged  by  the 
gravitational  water  passing  through  the  first  foot.  The 
downward  movement  of  water  is  comparatively  rapid  and 
largely  gravitational;  the  upward  movement  compara- 
tively slow  and  capillary.  Therefore,  in  irrigated  soils, 
fairly  rich  in  soluble  matters,  the  tendency  is  to  concen- 
trate the  soluble  materials  in  or  near  the  top  soil. 

Arid  soils  are  frequently  50  to  70  feet  deep  and  at  times 
that  distance  from  the  ground  water.  The  irrigation 
water  in  such  soils,  if  wisely  applied,  moves  downward  10 
to  15  feet.  It  is  only,  then,  within  this  limit  that  the 
soluble  matters  are  moved  upward.  If  the  soil  is  rich  in 
soluble  matters,  this  concentration  may  result  in  injury 
to  the  plants;  if,  as  is  the  usual  case,  the  percentage  of 
soluble  matters  is  low,  no  injury  results,  but  the  plant- 
foods  from  lower  depths  are  made  easily  available  to 
plants.  Even  where  the  soil  is  rich  in  soluble  materials, 
the  farmer  can,  by  judicious  irrigation,  and  by  the  proper 
cultivation  of  the  soil,  keep  the  soluble  substances  so 
well  distributed  that  no  damage  can  result  to  the  growing 
crop. 

58.  Salinity  of  river  waters. — The  natural  waters 
used  in  irrigation  are  never  quite  pure,  for  no  natural 
water  is  free  from  dissolved  substances.  Even  rain-water 
dissolves  from  the  air  considerable  quantities  of  nitrates 
and  other  substances.  When  the  water  that  falls  upon  the 
land  as  rain  or  snow  moves  toward  the  rivers  by  seeping 
through  the  soil  or  by  flowing  over  the  ground,  it  succeeds 
in  dissolving,  during  its  descent,  relatively  large  quanti- 
ties of  soil  materials.  The  more  deeply  such  water  soaks 
into  the  soil  before  it  finally  reappears  as  a  spring,  or  the 
longer  it  flows  over  the  soil,  the  higher  will  be  its  concen- 


SOIL  CHANGES  DUE  TO  IRRIGATION 


83 


tration  of  dissolved  substances.  This  is  well  shown  by 
any  of  the  analyses  made  of  river  water  taken  at  different 
distances  from  the  river  head.  For  instance,  in  the  fol- 
lowing rivers  the  salinity  or  the  parts  of  soluble  matter  in 
1,000,000  parts  of  water  was  as  follows: 


River 

Near  the 
head 

Lower 
down 

Cache  la  Poudre     

37 

1  Oil 

Arkansas  

148 

21,034 

Bear 

185 

637 

Jordan,  Utah 

892 

1  090 

Chalis,  Algeria 

6  670 

1  182 

The  Chalis  River,  Algeria,  is  an  exception  to  the  rule 
because  tributaries,  carrying  relatively  pure  water,  enter 
and  dilute  the  main  river  near  its  lower  end. 

The  quantity  of  dissolved  substances  in  natural  water, 
that  is,  the  salinity,  varies  from  exceedingly  small  quan- 
tities, as  in  rain-water,  to  almost  saturated  solutions,  as  in 
the  waters  of  the  Dead  Sea  and  the  Great  Salt  Lake.  The 
following  table,  based  upon  the  classical  work  on  "The 
Data  of  Geochemistry,"  by  F.  W.  Clarke,  shows  the  pro- 
portions of  dissolved  substances  found  hi  some  of  the 
river  waters  of  the  world.  No  such  table,  however  elabo- 
rately constructed,  can  be  wholly  accurate.  At  best,  only 
a  few  of  the  rivers  of  the  world  have  been  subjected  to 
chemical  analysis,  and  even  the  rivers  that  have  been 
most  thoroughly  studied,  have  not  been  analysed  at  all 
seasons  of  the  year  for  a  sufficient  number  of  years  to 
make  the  averages  absolute  in  their  values. 


IRRIGATION  PRACTICE 


DISSOLVED  SUBSTANCES  IN  RIVER  WATERS 
(Parts  per  million) 


Locality 

Range 

Remarks 

Min. 

Max. 

United  States- 
Atlantic  Slope      .... 
Mississippi  Basin     .    .    . 
Southwestern  rivers     .    . 
Northwestern  rivers    .    . 
Great  Basin  (no  outlet) 
California 

15 
90 
321 
31 
185 
119 

1 
115 

31 
134 
49 
126 
13 

37 
40 
130 

86 

140 
2,323 
2,384 
1,481 
1,090 
2,412 

298 
551 

286 
254 
447 
299 
221 

59 
9,185 
174 
122 

Nearly  all  under  100 
One-half  under  300 
Three-fourths  above  700 
Nearly  all  under  100 

Nearly  half  under  200 

Canada  — 
St.  Lawrence  Basin.    .    . 
Saskatchewan  Basin    .    . 
Europe  — 
Great  Britain    
"\Vestern 

Eastern      

Rhine     

Elbe   

South  America  — 
Amazon     

Southern 

Nile    . 

India  and  Java 

It  will  be  observed  that,  in  the  United  States,  the 
waters  of  highest  average  purity,  that  is,  of  lowest  con- 
centration, are  those  on  the  Atlantic  Coast;  those  of  the 
Mississippi  Basin  and  of  the  great  Northwest  come  next; 
the  waters  of  the  southwestern  rivers,  including  the 
Colorado,  are  still  higher  in  their  average  content  of  solu- 
ble matter;  while  those  of  the  California  rivers  stand 
between  those  of  the  Mississippi  River  and  those  of  the 
Southwest.  The  rivers  of  the  Great  Basin,  which,  after  a 
short  journey  from  the  mountain  headwaters,  reach  the 
interior  lake  into  which  their  load  is  deposited,  are  less 
concentrated  than  the  rivers  of  the  Southwest  and  more 
like  those  of  the  Mississippi  River  Basin. 


SOIL  CHANGES  DUE  TO  IRRIGATION  85 

The  concentration  of  river  waters,  at  least  in  the 
United  States,  appears  to  vary  with  the  rainfall.  In 
humid  districts,  where  the  soils  are  more  thoroughly 
water-washed,  and  where  the  run-off  is  large,  the  quantity 
of  dissolved  material  is  small.  In  arid  districts,  with 
soils  richer  in  soluble  matter,  the  concentration  of  the 
river  waters  increases.  While  the  annual  rainfall  is  not 
the  only  factor  determining  the  concentration  of  river 
waters,  yet  it  determines,  in  large  measure,  the  quantity 
of  soluble  substances.  The  same  general  law  may  be 
observed  in  the  data  dealing  with  the  Canadian  rivers. 
In  the  St.  Lawrence  Basin,  the  proportion  of  dissolved 
substances  in  the  river  waters  is  considerably  smaller 
than  in  the  Saskatchewan  Basin,  which  is  more  of  a  semi- 
arid  character.  Similarly,  the  data  from  the  river  waters 
of  Europe  shows  a  variation  with  the  general  climatic 
conditions,  especially  with  the  rainfall. 

The  Nile,  famous  in  irrigation  history,  does  not  carry 
a  great  abundance  of  soluble  material.  It  stands  in  this 
respect  between  the  waters  of  the  Mississippi  and  those 
of  the  Great  Basin.  The  data  of  the  above  table,  which 
are  representative  of  the  rivers  of  the  world,  show  that 
the  quantity  of  dissolved  substances  in  river  waters  is 
not  extraordinarily  large.  In  most  cases,  the  waters  of 
even  long  rivers  in  arid  districts  are  less  concentrated  than 
the  ordinary  drainage  water  of  agricultural  fields. 

The  river  waters  of  humid  regions,  with  low  total  con- 
centration, are  comparatively  rich  in  carbonates;  those 
of  arid  regions,  on  the  other  hand,  with  high  concentra- 
tion, contain  more  sulfates  and  chlorides  than  carbon- 
ates. This  is  explained  when  it  is  recalled  that,  under 
humid  conditions,  the  native  vegetation  grows  abundantly 
and  the  proportion  of  soil  humus  is  much  larger  than 


86  IRRIGATION  PRACTICE 

under  more  arid  conditions.  Water  passing  through  such 
humid  soils  naturally  takes  up  from  the  humus  much 
carbon  dioxide. 

59.  Salinity  of  lake  waters. — The  waters  of  the  great 
lakes   of   the  world,  from   which   irrigation   waters   are 
frequently  taken,  vary  as  largely  as  do  the  river  waters. 
The  water  of  mountain  lakes  that  are  fed   directly  by 
the  melting  snows  contains  little  dissolved  matter.    For 
example,  the  water  of  Lake  Tahoe,  in  Nevada,  contains 
only  73  parts  of  dissolved  substances  to  1,000,000  parts 
of  water;  whereas,  the  water  of  Sevier  Lake,  in  Utah,  con- 
tains 86,400  parts,  and,  in  the  water  of  the  Great  Salt 
Lake  there  are  nearly  300,000  parts  of  dissolved  sub- 
stances.    Ocean    water,    as    another    example,    contains 
about  39,000  parts  of  dissolved  substances  in  1,000,000 
parts  of  water.     Naturally   the  lakes  that  contain  the 
most  concentrated  solutions  are  in  almost  every  instance 
those  of  interior  basins  with  no  outlet  to  the  ocean.    The 
water  runs  into  these  basins  and  as  it  is  gradually  evap- 
orated it  leaves  behind  its  load  of  soluble  materials  to 
concentrate  the  remaining  water.    In  the  course  of  time, 
such  waters   become  saturated  with   certain  substances 
which  then  crystallize  out.  This  is  the  case  with  the  Great 
Salt  Lake  and  many  other  well-known  interior  lakes  of 
western  United  States  and  other  arid  parts  of  the  world. 

60.  Salinity  of  mineral  springs. — The  most  heavily 
charged  waters,   however,   save  those  of  interior  basin 
lakes,  issue  as  mineral  springs  in  many  parts  of  the  world. 
The  high  degree  of  salinity  of  such  waters  seems  to  be 
due,  as  already  suggested,  to  the  fact  that  the  percolated 
water  has  passed  over  subterranean  layers  of  soluble 
material  which  is  brought  up  in  solution  when  the  spring 
issues  from  the  soil.    The  salinity  of  such  waters  varies 


SOIL  CHANGES  DUE  TO  IRRIGATION  87 

from  extreme  purity  to  a  concentration  comparable  with 
saturated  waters  of  inland  lakes. 

61.  Soil  moisture  and  natural  waters  compared. — As 
shown  above,  the  soil  solution  of  a  clayey  loam  contain- 
ing about  .1  per  cent  of  soluble  matter  will  contain  in  the 
neighborhood  of  5,000  parts  of  dissolved  matter  for  1,000,- 
000  parts  of  water.    This  is  considerably  higher  than  the 
concentration  of  the  larger  number  of  river  waters,  or  even 
of  mineral  springs.   In  the  arid  regions,  the  soluble  matter 
of  soils  often  exceeds  .1  per  cent,  and  the  concentration 
of  the  soil  solution,  after  irrigation,  is  probably  higher 
than  5,000.    Moreover,  if  the  top  soil  is  not  thoroughly 
stirred,  evaporation  from  the  soil  surface  goes  on  very 
rapidly  and  the  soil  solution  becomes   so  concentrated 
that,  before  the  next  irrigation,  the  concentration  must  be 
nearly  twice  what  it  is  immediately  after  an  irrigation. 
The  effect  of  varying  quantities  of  dissolved  substances 
in  irrigation  water  on  the  growth  of  plants  will  be  dis- 
cussed in  the  chapter  on  alkali.    It  is  of  very  great  impor- 
tance to  the  irrigation  farmer. 

62.  Ash   constituents  added   by   irrigation  water. — 
When  the  quantities  of  water  used  in  irrigation  are  so 
large  that  there  is  a  constant  drainage  through  the  soil, 
the  only  probable  effect  of  the  water  on  the  soil  is  the  wash- 
ing out  of   certain   soil   constitutents.     When  water  is 
added  in  moderation,  so  that  the  soil  is  filled  to  a  certain 
depth,  but  not  in  sufficient  quantity  to  drain  through,  the 
soluble  matters  contained  by  the  water  must  of  necessity 
remain  in  the  soil,  except  as  they  may  be  utilized  by  the 
plant.       Under  existing  practices  2  acre-feet  of  water 
represent  a  very  moderate  annual  irrigation.    On  suffi- 
ciently deep  soils,  if  the  single  applications  are  not  too 
large,  this  quantity  of  water  does  not  cause  material 


88  ^IRRIGATION  PRACTICE 

drainage.  It  is  then  possible  to  calculate  the  probable 
quantities  of  soluble  salts  deposited  in  the  soil  to  a  depth 
of  10  to  15  feet  during  one  season's  irrigation.  In  the 
arid  regions,  250  parts  of  dissolved  substances  in  1,000,000 
parts  of  water  are  accounted  unusually  low,  unless  obnox- 
ious substances  are  admixed.  Such  a  water,  applied  to  the 
soil  to  a  depth  of  2  feet  throughout  the  season,  allowing 
for  no  drainage,  would  leave  in  an  acre  of  soil  throughout 
the  season,  approximately  1,300  pounds  of  solid  matter. 
This  repeated,  year  after  year,  would  naturally  run  into 
large  amounts,  although  some  would,  undoubtedly,  be 
taken  up  by  the  plants  in  their  growth  and  used  for  the 
elaboration  of  plant  tissues. 

At  the  Utah  Station,  a  large  number  of  analyses  were 
made  of  crops  grown  under  irrigation,  and  it  was  found 
that  in  wheat  kernels  the  ash  content  was  about  2.5  per 
cent  and,  in  wheat  straw,  about  10  per  cent.  A  thirty- 
bushel  wheat  crop  would  then  abstract  from  the  soil 
about  345  pounds  of  mineral  matter,  or  a  little  more  than 
one-fourth  of  the  total  quantity  added  by  irrigation. 
Lucern  contained  about  8.5  per  cent  of  ash  materials,  in 
which  case  a  crop  of  10,000  pounds  would  contain  approx- 
imately 850  pounds,  or  a  little  more  than  two-thirds  of 
the  materials'  left  by  the  irrigation  water.  None  of  the 
crops  ordinarily  grown  under  irrigation  takes  up  the 
quantity  of  soluble  substances  added  to  the  soil  by  2 
acre-feet  of  water,  providing  drainage  is  prevented.  It 
must  be  remembered,  in  this  connection,  that  irrigation 
waters  do  not  always  contain  all  the  essential  plant-foods, 
or  in  the  right  proportion.  While  a  water  may  add  to 
the  soil  more  solid  matter  than  the  crop  needs,  the  indi- 
vidual constituents  may  be  wholly  or  in  part  absent,  and 
must  be  supplied  by  the  soil. 


SOIL  CHANGES  DUE  TO  IRRIGATION  89 

Under  more  modern  and  improved  methods  of  irriga- 
tion, first-class  crops  are  frequently  raised  with  1  or  1J^ 
acre-feet  of  water.  In  such  cases,  the  crop  more  nearly 
takes  up  the  substances  added  to  the  soil  by  irrigation 
water.  On  the  other  hand,  the  water  used  for  irrigation 
ordinarily  contains  more  than  250  parts  of  dissolved  sub- 
stances hi  1,000,000  parts  of  water.  If  the  salinity  is  500, 
2  acre-feet  of  water  would  add  to  one  acre,  2,600  pounds 
of  solid  substances,  and  waters  richer  hi  mineral  matters 
would  leave  hi  the  soil  tremendous  quantities  of  solid 
matters.  It  is  readily  seen,  therefore,  how  profoundly 
irrigation  water  may  affect  soils  under  irrigation.  Should 
the  irrigation  water  be  heavily  charged  with  substances 
deleterious  to  soil  or  crop,  immediate  and  irreparable 
damage  may  be  done.  Little  definite  information  con- 
cerning the  whole  subject  is  as  yet  available.  It  is  quite 
evident,  however,  that  the  methods  of  irrigation  must  be 
varied  with  regard  to  the  composition  of  the  water  used. 

63.  Use  of  concentrated  waters. — An  irrigation  water 
of  medium  concentration  may  be  used  safely  in  modera- 
tion, although  it  should  be  so  used  as  to  leave  as  little  as 
possible  of  its  constituents  in  the  soil.  When  concentrated 
waters  are  used,  excessive  quantities  are  applied  to  force 
drainage,  so  that  the  concentration  of  the  free  water  in 
the  soil  after  irrigation  is  never  above  that  of  the  water 
used.  This  is  the  good  reason  behind  the  practice  of 
farmers,  in  districts  where  the  soils  or  waters  are  heavy 
in  alkali,  to  use  more  water  throughout  the  season  than 
in  districts  where  the  soils  are  freer  from  alkali  and  the 
water  of  low  concentration.  This  principle  is  frequently 
the  essential  one  in  building  up  a  district  which  of  neces- 
ity  must  depend  upon  highly  mineralized  water  for  its 
supply  of  irrigation  water. 


90  IRRIGATION  PRACTICE 

64.  Need   of  water   surveys. — The   substances   con- 
tained by  the  water  may  in  themselves  be  harmless ;  but, 
since  they  are  applied  to  the  soil  from  year  to  year  in 
such  large  quantities,  they  undoubtedly  often  fill  many  of 
the  capillary  soil  spaces  or  are  deposited  on  the  surfaces 
of  the  soil  grains,  and  thus  affect  the  chemical  composi- 
tion and  the  granular  condition  of  the  soil.    This  subject 
has  as  yet  been  poorly  investigated,  but  is  worthy  of 
careful  investigation,  so  that  irrigation  practices  may  be 
rationalized  from  the  point  of  view  of  the  varying  com- 
position of  irrigation  water.     Systematic  chemical  sur- 
veys of  irrigation  waters  should  be  made  in  connection 
with  the  study  of  the  soils  to  which  the  waters  are  to  be 
applied.    Only  when  such  data  are  abundantly  at  hand 
will  it  be  possible  to  formulate  for  each  section  irrigation 
practices  that  will  be  permanently  satisfactory.    In  the 
present  stage  of  irrigation  progress,  it  has  become  very 
important  to  know  the  composition  of  irrigation  waters. 
As   irrigation   becomes   older   more  problems  will   arise, 
many  of  which  can  be  solved  only  by  a  more  thorough 
knowledge  of  the  waters  used  on  irrigated  soils.   Water 
surveys  are  as  legitimate  in  irrigated  districts  as  are  soil 
surveys. 

65.  Composition  of  natural  waters. — While  the  total 
quantity  of  soluble  matter  found  in  a  given  volume  of 
irrigation  water  is  of  great  importance,  the  composition 
of  such  soluble  matter  is  of  equal  importance.    In  soils 
are  found  the  great  majority  of  the  chemical  elements 
and  particularly  those  that  are  essential  in  plant-growth. 
In  the  following  table  may  be  found  the  composition  of  a 
number  of  natural  waters  selected  from  the  data  given 
by  Clarke. 


SOIL  CHANGES  DUE  TO  IRRIGATION 


91 


"tf-rTj} 

£ 

.    2.       .  .  .  :  . 

a 

'    a  ' 

I—                                   tO               •—  CO 
H-tO        tOCnCoppentOCn 

5  en        to  CD  £  0  O  OC  £  Cn 

1.  —  River  waters 
Average  for  world. 
—  F.  W.  Clarke 

'Z. 

P->             >-*             tO    *>• 

•     p       p  ^  co  co  •     to  co  j-i 
CO        <iobij^.     Cn  <l  Cn 
CO         -*4  tO  tO  CO         O  CO  ^ 

2.  —  Rio  Grande 
at 
Messilla,  N.  M. 

-: 
I 

I—  >         t—  '         I—  i  I—  '  tO 
•      •            OC  Cn  CO  p  •      <J  CO  p 

>—  co  b>  to  .    b  cc  co 

O  OC  ^  O         H-  C5  t- 

3.—  Snake  River 
at 
Blackfoot,  Idaho 

7. 

0 

ZL 

_                _                :  ^     _     _ 

4.  —  San  Joaquin 

•< 

0000         ®2SSw^Sntw 

Lathrop,  Calif. 

I 

•      •            J-  p  CO  H-  •      S  -^  p 
»—  *  Cn  M  tO  .      rf^  Oi  tO 

H-  CO  CO  O         00  CO  I— 

5.  —  Ocean  water. 
Challenger 
expedition 

~^ 

•     •           CO  to  i—  O  •     Cn  Ci  • 

H-  CO  CO  I-1       •"  k->   O 
CO  V|  O5  <l          1—  O5 

6.—  Great  Salt 
Lake  water 

CC                         Ci 

.  p     •   H-  H-  *>  •  r*  p  • 

7.—  Chloride 
water 

p  •        p  j-1  to  p  •    to  to  • 
b  .        to  to  ~a  en  .    o  en  . 

en           to  co  co  co       to  o 

8.—  Sulphate 
water 

to               en 
to  co      o  t-»  co  so  •    toocn 

9.  —  Carbonate 

_^    Q^             -<|    ^    HU    ^              ^  _    Q^    ^Q 

toto       cotoenoc'     torf^to 

water 

i-  co      to 

cC  O        O  ^*J  C^  Cn  O  C^  *^J  IO 

10.—  Nitrate 
water 

1 

s. 

r 

\ 
$ 


92  IRRIGATION  PRACTICE 

The  first  column  shows  the  average  composition  (rarer 
elements  being  excluded)  of  river  waters  for  the  world. 
All  the  elements  necessary  for  plant-growth  are  present. 
The  carbonic  acid,  combined  chiefly  with  calcium,  is  in 
largest  abundance.  Sulfuric  acid,  in  combination  with 
calcium,  magnesium,  sodium  and  possibly  potassium,  is 
also  present  in  large  abundance.  Chlorine  is  third  in 
abundance.  Even  nitric  acid,  vitally  important  for  plant- 
growth,  is  present  in  small  quantities.  In  the  three  fol- 
lowing columns  are  analyses  of  the  waters  of  three  great 
rivers  of  western  America,  used  largely  for  irrigation  pur- 
poses. All  the  necessary  plant-foods  are  present,  but  in 
very  different  proportions,  which,  undoubtedly,  will 
affect,  differently,  the  conditions  of  plant-growth.  In 
column  5  is  the  average  composition  of  ocean  waters  as 
determined  by  the  Challenger  expedition.  It  differs 
materially  from  the  analysis  in  column  1  which  is  a  world 
average  for  river  water.  The  carbonic  acid  has  practically 
disappeared,  no  doubt  precipitated  by  the  lime,  and  the 
sodium  and  chlorine  have  increased  tremendously.  In 
column  6  is  an  analysis  of  the  water  of  the  Great  Salt 
Lake,  which  is  a  body  of  water  practically  saturated  with 
common  salt.  It  resembles  ocean  water,  but  carbonic 
acid  is  totally  absent;  the  proportion  of  calcium  and 
magnesium  lower;  of  potassium  higher. 

66.  Classification  of  natural  waters. — Considering 
the  composition  of  the  soluble  materials  held  by  natural 
waters,  especially  those  used  in  irrigation,  they  may  be 
classified  as  follows:  Those  rich  in  chloride  of  sodium  are 
called  chloride  waters;  those  rich  in  sulfates,  especially 
of  sodium  and  calcium,  are  sulfate  waters;  those  rich  in 
carbonates,  especially  of  sodium,  are  carbonate  waters; 
those  rich  in  borates  are  borate  waters;  those  rich  in  free 


SOIL  CHANGES  DUE  TO  IRRIGATION  93 

acids,  are  add  waters.  This  classification  may  be  extended 
to  cover  any  water  as  soon  as  its  predominating  con- 
stituent is  known.  The  above  are  the  leading  classes.  A 
typical  analysis  of  a  water  in  several  of  the  above  classes 
will  be  found  in  the  last  four  columns  of  the  preceding 
table. 

This  classification  of  natural  waters  is  very  useful  in 
irrigation  practice,  and  especially  important  in  consider- 
ing the  alkali  question.  For  the  purposes  of  this  chapter 
it  is  sufficient  to  make  clear  that  practically  all  known 
natural  waters,  unless  rain-water  and  water  coming 
immediately  from  the  melted  snow  be  excepted,  contain 
varying  quantities  of  all  the  essential  elements  of  plant- 
growth.  Moreover,  the  variations  in  the  proportions  of 
the  constituents  of  water  are  so  great  that  while  the  waters 
may  be  roughly  classified  as  chloride,  sulfate  or  car- 
bonate waters,  there  is  a  host  of  intermediate  kinds  which 
overlap  two  or  more  groups.  For  an  exact  understanding 
of  the  chemical  behavior  of  an  irrigation  water  on  the 
soil  or  crop,  an  analysis  of  the  water  in  question  must 
be  available. 

67.  Plant-food  value  of  irrigation  water.— The  infor- 
mation found  in  the  preceding  table  makes  possible  some 
interesting  calculations.  The  quantity  of  plant  nutrients, 
such  as  nitrogen,  potassium,  phosphorus  and  lime  removed 
from  an  acre  of  soil  by  some  of  the  common  crops,  has  been 
computed  by  Warington.  His  results,  obtained  under 
humid  conditions,  do  not  differ  greatly  from  those  that 
might  be  obtained  under  irrigated  conditions,  and,  until 
data  from  irrigated  crops  are  obtained,  may  be  used  with 
approximate  accuracy.  A  crop  of  wheat  yielding  thirty 
bushels  to  the  acre  requires  at  least  about  thirty  pounds  of 
potash,  ten  pounds  of  lime,  twenty  pounds  of  phosphoric 


94  IRRIGATION  PRACTICE 

acid  and  forty-eight  pounds  of  nitrogen.  By  using  the 
smallest  percentage,  22  per  cent  of  potash,  in  the  above 
table,  2  acre-feet  of  water  would  yield  a  little  less  than  six 
pounds  of  potash,  a  quantity  entirely  insufficient  for  the 
production  of  a  crop.  By  using  the  averages  of  some  of  the 
other  waters  in  the  table,  the  potash  added  by  2  acre- 
feet  is  ample  to  supply  the  crop  needs.  Any  of  the  waters 
in  the  table,  save  No.  6,  with  only  17  per  cent  lime,  would 
supply  amply  the  needs  of  the  crop  for  lime.  In  most 
waters,  the  nitric  acid  is  present  in  natural  waters  in  very 
small  quantities,  but  it  is  not  likely  that  the  quantity 
of  water  ordinarily  used  in  irrigation  throughout  a  season 
would  be  sufficient  to  supply  the  crop  needs.  Phosphoric 
acid  is  also  present  in  small  quantities  and  seldom  can 
supply,  thoroughly,  the  crop  needs.  While,  therefore,  the 
total  soluble  material  contained  by  ordinary  water 
appears  to  be  quite  sufficient  in  quantity  to  supply  the 
total  needs  of  the  plant,  the  specific  substances  required 
for  successful  plant-growth  are  fully  met  only  in  a  few 
waters.  With  moderate  irrigations  and  waters  of  aver- 
age composition,  plants  must  draw  upon  the  soil  for  at 
least  some  of  the  constituents  needed  in  their  growth — 
notably  for  phosphoric  acid,  nitrogen  and  potash.  Waters 
in  which  these  substances  are  present  in  larger  propor- 
tions may  supply  all  the  needs  of  the  crop  for  mineral 
matters. 

The  property  of  the  soil  to  retain  certain  ingredients 
of  the  water  that  may  be  passing  through  it  is  of  impor- 
tance in  this  connection.  Lime,  magnesia,  potash  (notably 
in  clay  soils),  chlorine,  and  practically  all  the  ingredients 
of  irrigation  water,  are  partly  absorbed  by  the  soil  through 
which  the  water  passes.  The  substances  that  are  absorbed 
and  the  degree  of  absorption  are  determined  by  the  com- 


SOIL  CHANGES  DUE  TO  IRRIGATION 


95 


position  of  the  soil  and  of  the  water.  To  establish  equilib- 
rium between  the  soil  and  the  water,  in  conformity  with 
chemical  and  physical  laws,  substances  dissolved  in  the 
irrigation  water  are  absorbed  and  held  by  the  soil,  or 
corresponding  substances  are  taken  from  the  soil  to 
enrich  the  drainage  water.  Because  of  this  soil  power  of 
absorption,  the  water  that  drains  from  the  soil  is  propor- 


FIQ.  18.  Badly  corroded  ditch  due  to  excessive  fall.    On  a  larger  scale  this  is  the 
action  of  swift  rivers. 

tionally  of  a  much  different  composition  from  the  water 
which  was  originally  added  to  the  soil.  This  is  brought 
out  by  the  analysis  on  page  77. 

68.  Suspended  matter  in  river  waters. — By  far  the 
larger  part  of  river  waters  carry  not  only  large  quan- 
tities of  dissolved  substances;  they  carry,  also,  considera- 
ble loads  of  suspended  solid  matter.  This  suspended 
material  is  naturally  derived  from  the  washing  effect  of 


96 


IRRIGATION  PRACTICE 


the  snow-water,  rain-water  and  floods,  chiefly  among  the 
highlands,  near  the  headwaters  of  the  river  course.  Note 
the  following  table : 

SUSPENDED  MATTER  IN  RIVER  WATERS 
(Parts  per  million) 


River 

Minimum 

Maximum 

Belle  Fourche,  at  Belle  Fourche,  S.  D.     ... 
Bighorn   at  Fort  Custer   Mont 

56 

18 

7,120 
2  860 

Colorado   at  Yuma  Ariz. 

741 

30,800 

Red,  at  Mangun   Okla.            

0 

16,800 

Gunnison,  at  Whitewater,  Colo  

32 

4,090 

Pecos   at  Carlsbad   N   M 

o 

1  480 

Pecos,  at  Dayton,  N.  M  
Rio  Grande   at  El  Paso   Texas 

44 

8 

11,400 
83  900 

Salt   at  Roosevelt  Ariz 

40 

6,940 

North  Platte,  at  Laramie  Wyo.    ... 

62 

3,450 

The  quantity  of  suspended  matter  as  shown  in  the 
above  table  is  very  variable  and  frequently  very  large. 
Rivers  rising  in  well-forested  districts,  or  those  that 
travel  only  a  short  distance  before  they  empty  into  the 
lake  or  main  river,  are  often  comparatively  free  from  sus- 
pended matter.  The  Colorado  and  the  Rio  Grande  Rivers 
carry  more  suspended  matter  than  any  other  of  the  great 
rivers  of  the  United  States.  As  shown  above,  as  high  as 
84,000  parts  of  suspended  matter  in  1,000,000  parts  of 
water — nearly  8.5  per  cent — have  been  found  in  the  water 
of  the  Rio  Grande  at  El  Paso,  Texas.  The  Colorado  at 
Yuma,  Arizona,  has  carried  nearly  31,000  parts,  or  more 
than  3  per  cent,  of  suspended  matter  in  1,000,000  parts  of 
water.  When  the  immense  volumes  of  water  in  such  rivers 
are  considered,  it  is  readily  understood  that  quantities  of 
suspended  matter  almost  beyond  human  comprehension, 
are  carried  from  the  highlands  tributary  to  the  river, 


SOIL  CHANGES  DUE  TO  IRRIGATION 


97 


FIG.  19.  Walled  ditch  to  prevent  erosion  of  easily  "washed" 
soil. 

during  each  season's  flow.   Large  rivers,  all  over  the  world, 
carry  similar  loads  of  suspended  matter.    Famous  exam- 
ples are  the  Nile,  the  Danube,  the  Rhine  and  many  other 
G 


98  IRRIGATION  PRACTICE 

historical  rivers,  a  large  number  of  which  are  partially 
diverted  for  irrigation  purposes.    (Figs.  18,  19.) 

69.  Seasonal  variation  of  suspended  matter. — The 
suspended  matter  carried  by  a  river  varies  in  quantity 
from  month  to  month.  This  is  well  shown  in  the  follow- 
ing table,  constructed  from  the  records  of  the  Green 
River,  at  Jensen,  Utah,  during  the  years  1905  and  1906. 

SUSPENDED  MATTER  CARRIED  BY  THE  GREEN  RIVER,  AT  JENSEN, 
UTAH,  EACH  MONTH  DURING  THE  YEAR  1905-06. 

(In  parts  per  million) 

April 2,278  October 666 

May      917  November 79 

June 415  December 64 

July       91  January 17 

August 613  February      28 

September 4,749  March 3,170 

In  March  and  April,  during  the  time  of  the  heavy 
spring  rains,  the  loads  of  sediment  were  very  large;  as 
also  in  September  and  October,  when  the  fall  rains 
occurred.  During  the  summer  months  of  June,  July  and 
August,  when  only  occasional  showers  fell,  the  suspended 
matter  was  low;  and  in  November,  December,  January 
and  February,  when  the  ground  was  largely  covered  with 
snow,  it  was  even  smaller. 

During  the  seasons  of  the  year  when  the  lands  around 
the  headwaters  of  the  rivers  are  not  covered  with  snow 
and  ice,  the  quantity  of  suspended  matter  carried  by  a 
river  varies  directly  with  the  time  and  quantity  of  pre- 
cipitation. A  sudden  flood  will  render  the  river  turbid 
with  suspended  matter,  and  the  longer  seasonal  floods  of 
spring  and  fall  are  characterized  by  long  periods  of  muddy 
water.  In  a  part  of  the  western  United  States  where  the 
growing  season  is  rainless,  the  water  is  clearer  during  the 


4400 


Fio.  20.  Daily  discharge  of  Malheur  River  (second-feet). 


FIG.  21.  Daily  discharge  of  Mackenzie  River  (second-feet). 

(99) 


100  IRRIGATION  PRACTICE 

irrigation  season  than  either  just  before  or  after.  In  other 
parts,  where  summer  rains  prevail,  the  irrigation  water 
is  often  heavily  loaded  with  suspended  matter.  (Figs. 
20,  21.) 

70.  Suspended  matter  added  to  soil  by  irrigation. — 
Considerable  quantities  of  sediment  may  be  added  to  the 
soil  during  a  season's  irrigation.    If  2  acre-feet  of  water 
are  used  annually  for  the  production  of  crops,  a  calcula- 
tion may  be  made  similar  to  that  which  was  made  con- 
cerning the  soluble  matter  added  to  the  soil.    During  the 
time  of  summer  floods,  few  waters  contain  less  than  1,000 
parts  of  suspended  matter  in  1,000,000  parts  of  water.   If 
this   were   continued   throughout   the   season,    it   would 
mean  an  addition  to  each  acre  of  land  of  over  5,000 
pounds   of   sediment.     The   southwestern   rivers,   which 
carry,  ordinarily,  throughout  the  season  much  more  sedi- 
ment than  this,  add  to  each  acre  during  each  irrigating 
season  an  extremely  large  total  quantity.    It  has  been 
reported   from   Arizona   that,    frequently,   the   sediment 
of  one  season's  irrigations  covers  the  land  to  a  thickness 
of  4  to  6  inches.     In  rivers  with  less  sediment,  these 
effects  are  not  so  visible,  but  wherever  irrigation  is  prac- 
tised, especially  in  arid  districts,  a  large  quantity  of  solid 
matter  is  deposited  on  and  in  the  soil.    This,  continued 
year  after  year,  will  certainly  affect  the  productive  power 
of  the  soil. 

71.  Suspended  matters  derived  from  surface  soils. — 
The  suspended  matters  in  river  waters  come  chiefly  from 
the  surface  washings  of  the  lands  near  the  headquarters  of 
the  rivers.    The  character  of  the  suspended  matters  car- 
ried by  rivers  varies,  therefore,  with  the  surface  nature 
of  the  soils  from  which  the  sediments  are  derived.    If  the 
contributing  soils  are  sandy,  the  suspended  matter  will 


SOIL  CHANGES  DUE  TO  IRRIGAT 

be  sandy;  if  the  soils  are  loamy  or  clayey,  the  sediments 
will  be  correspondingly  more  rich  in  clayey  materials. 
Usually,  however,  only  the  silty  or  finer  particles  reach 
the  lower  portions  of  the  river  where  the  irrigation  canals 
are  taken  out.  The  coarser  or  more  sandy  particles  are 
deposited  in  the  first  quiet  places  of  the  river  and  do  not, 
ordinarily,  reach  the  lower  lands,  except,  perhaps,  in 
times  of  high  water,  when  even  the  sand  deposits  of  earlier 
years  may  be  torn  up  and  whirled  down  to  the  irrigated 
districts. 

The  top  or  surface  soil  is  always  most  vigorously 
affected  by  sunshine,  air,  water  and  biological  agencies; 
therefore  the  top  soil  is  the  most  fertile  part  of  the  soil. 
It  is  this  fertile  soil  layer  that  is  washed  into  the  rivers, 
finally  perhaps  to  be  deposited  on  the  farmers'  fields. 
Eventually,  then,  the  farmer  covers  his  own  land  with  the 
fertile  surface  soil  of  the  mountain  slopes  and  upland 
valleys. 

72.  Composition  of  river  sediments. — River  sediments 
have  been  analysed  in  the  United  States,  in  Europe  and 
in  Egypt.  The  results  show  that  river  muds  are  somewhat 
richer  in  the  essential  plant-foods  than  the  ordinary 
fertile  soils  which  the  water  serves.  It  has  been  estimated 
by  Forbes  that  the  market  value  of  the  fertilizing  con- 
stituents in  three  samples  of  Salt  River  mud,  to  the  acre- 
foot  of  water,  varied  from  $7.98  to  $25.51.  These  figures 
should  be  given  respectful  consideration  by  the  farmer 
who  does  not  content  himself  with  using  one  acre-foot 
of  water.  When  the  fertilizing  value  of  these  sediments 
is  considered  in  connection  with  the  fertilizing  value  of 
the  dissolved  materials,  one  of  the  great  advantages  of 
irrigation  is  made  evident.  Under  many  of  the  rivers  of 
the  irrigated  section,  proper  methods  of  irrigation  should 


102 


IRRIGATION  PRACTICE 


make  the  draft  of  the  plant  upon  the  soil  so  small  as  to 
extend  greatly  the  productive  power  of  the  soil. 

73.  Physical  effects  of  sediments. — The  physical 
effects  of  the  addition  of  river  silts  to  the  soil  are  not, 
however,  always  uniformly  beneficial.  On  a  sandy  soil, 
the  river  silts  usually  bind  the  soil  together  and  make  it 
more  firm,  of  better  water-holding  power  and  of  easier 


FIG.  22.  Deposit  in  field  of  suspended  matter  from  irrigation  water. 

cultivation.  On  a  heavy  clay,  if  the  river  sediment  is  of 
a  loamy  character,  the  clay  is  mellowed  and  lightened 
and,  therefore,  improved.  However,  if  the  silt  is  very 
fine  or  of  a  clayey  nature,  its  application  to  a  clay  soil 
or  even  to  a  loam  soil  might  be  disadvantageous,  because 
of  the  finer  texture  that  it  would  produce.  Herein  lies 
the  danger  in  using  irrigation  water  that  carries  consider- 
able quantities  of  suspended  matter.  River  mud  is  usually 


SOIL  CHANGES  DUE  TO  IRRIGATION  103 

of  a  very  fine  texture.  When  dry,  it  crusts  and  forms  a 
hard  covering,  which  does  not  readily  admit  water  or  air 
into  the  soil.  This  necessarily  interferes  seriously  with 
plant-growth.  One  season's  irrigation  is  not  greatly 
injurious,  but  if  repeated  year  after  year,  unless  proper 
cultural  treatments  are  employed  it  may  result  disas- 
trously. 

Another  danger,  of  less  importance,  resulting  from  the 
use  of  water  containing  much  suspended  matter,  is  that 
occasionally  the  finely  suspended  matter  clings  closely 
around  the  roots  of  the  plant,  and,  as  it  dries  and  con- 
tracts, injures  the  plant  mechanically;  or  it  may  produce 
a  type  of  sun-scald,  not  yet  clearly  understood.  It  is 
not  wise  to  apply  to  young  plants  during  a  period  of 
high  temperature  an  abundance  of  water  heavily  charged 
with  suspended  matter.  (Fig.  22.) 

74.  Cultural  treatment  of  sediments. — It  is  not, 
however,  a  very  difficult  problem  to  meet  and  overcome 
this  condition.  The  annual  silt  deposit  should  be  plowed 
into  the  soil  thoroughly  each  fall  or  spring,  and,  to  keep 
the  top  soil  open,  thorough  cultivation  should  be  prac- 
tised throughout  the  growing  season.  It  has  been  observed 
that  fields  of  wheat,  irrigated  with  water  rich  in  mud, 
have  produced  unusually  large  crops  wherever  the  sedi- 
ment was  plowed  in  from  year  to  year,  and  the  soil  thor- 
oughly disked  or  harrowed  in  the  spring  after  the  high- 
water  irrigation,  with  its  load  of  silt,  had  been  applied. 
The  young  wheat  is  not  injured  materially  by  such  early 
harrowing,  and  the  advantages  resulting  from  the  breaking 
of  the  silt  crust  are  shown  in  unusually  large  crops.  On 
the  other  hand,  an  alfalfa  field,  cultivated  in  the  old- 
fashioned  way,  that  is,  which  receives  no  cultural  help 
throughout  the  season,  is  soon  made  to  suffer  severely 


104  IRRIGATION  PRACTICE 

by  the  accumulation  of  the  annual  silt  deposits,  which 
effectually  shut  out  air  from  the  soil  and  make  it  almost 
impossible  for  water  to  penetrate  into  the  lower  soil 
layers.  If  this  one  danger  be  avoided,  the  suspended 
matter  in  irrigation  waters  may  be  made  a  source  of  wealth 
to  the  irrigation  farmer. 

75.  Effect  of  sediments  on  crop  yields. — Forbes  has 
made  some  interesting  experiments  on  the  effects  of  the 
river  silt  on  the  production  of  crops  in  Arizona.    Similar, 
but  not  so  carefully  made,  observations  have  been  made 
in  other  sections  of  the  world.    The  general  conclusion 
seems  to  be  that  wherever  water,  carrying  sediments,  is 
applied  without  attention  being  given  the  silt  deposits, 
the  crop-yields  tend  to  decrease.    Whenever,  however, 
the  physical  disadvantages  discussed  above  are  offset  by 
proper  tillage,  great  financial  advantages  result  from  the 
fertile  matter  carried  by  the  irrigation  waters.    In  fact, 
the  fertile  suspended  matters,  carried  at  the  irrigation 
season,   should  increase  materially  the  value  of  water- 
rights  from  such  sources.    The  tremendous  value  of  the 
overflow  of  the  Nile,  heavy  with  suspended  matter  brought 
from  the  African  highlands,  is  a  familiar  historical  fact. 
In  India,  South  Africa,  Europe  and  the  United  States, 
there  are  districts  in  which  the  lands  have  higher  values 
because  of  the  quantities  of  sediment  carried  by  the 
irrigation  streams. 

The  irrigation  farmer  deals  with  a  much  more  compli- 
cated problem  than  does  his  brother  who  depends  simply 
upon  the  natural  precipitation  for  the  moisture  supply. 
To  the  irrigation  farmer  the  soil  is  one  factor,  the  rainfall 
another,  and  the  water  that  he  uses  may  be  almost  as 
important  a  factor  as  the  soil  itself. 

76.  Water  and  soil  life. — Soil  moisture  also  exerts  a 


SOIL  CHANGES  DUE  TO  IRRIGATION  105 

distinct  effect  on  the  living  organisms  in  the  soil.  The 
detailed  relations  that  exist  between  soil  life  and  varying 
soil  moisture  are  yet  to  be  determined,  and  will  furnish 
another  and  most  important  chapter  in  irrigation  practice. 
Very  few  investigations  have  been  made  on  this  phase  of 
irrigation,  although  the  field  is  full  of  promise. 

It  is  well  known  that  bacteria  and  other  forms  of  low 
life  flourish  best  when  in  the  presence  of  an  abundance  of 
water,  and  the  statement  is  commonly  made  that  the 
greatest  effects  of  bacterial  life  are  obtained  when  an 
excess  of  water  is  available.  While  these  findings  are 
generally  true,  it  must  be  observed  that  few  studies  of 
bacterial  activity  have  been  made  under  an  environment 
similar  to  that  which  prevails  in  the  soil.  Low  forms  of 
life,  like  higher  ones,  require  various  foods  in  addition  to 
water;  and  these  substances  must  be  in  solution  at  a 
certain  concentration.  Under  irrigation,  as  already  shown, 
the  concentration  of  the  soil  solution  may  be  varied  con- 
siderably. When  over-irrigation  is  practised,  the  soil 
solution  is  kept  very  dilute;  when  no  irrigation  is  prac- 
tised, during  rainless  summers,  it  may  be  kept  very  con- 
centrated. This  phase  of  the  subject,  in  relation  to  soil 
life,  is  yet  to  be  studied. 

Stewart  and  Greaves  have  studied,  at  the  Utah  Sta- 
tion, the  effect  of  varying  applications  of  water  on  the 
nitrifying  organisms.  Series  of  field  plats  were  grown  to 
different  crops.  Each  series  received  irrigation  from  25 
inches  to  none.  The  soil  was  ideally  adapted  to  rapid 
bacterial  action.  The  work  was  continued  over  eight 
years,  so  that  the  conclusions  may  be  accepted  with  con- 
siderable assurance  of  their  truth.  It  was  found  that 
the  nitric  nitrogen  content  never  exceeded  300  pounds  to 
a  depth  of  10  feet.  The  application  of  irrigation  water 


106  IRRIGATION  PRACTICE 

had  a  distinctly  beneficial  effect  upon  the  formation  of 
nitric  nitrogen.  The  greatest  total  production  was 
observed  when  15  inches  of  water  were  applied.  The 
greatest  production  to  the  inch  of  water  was  found,  how- 
ever, when  the  minimum  quantity  of  water  was  used.  The 
use  of  the  maximum  quantity  of  water,  25  inches,  decreased 
the  total  yield,  and  gave  the  smallest  yield  of  nitrates  per 
inch  of  water  used.  A  medium  quantity  of  water  appeared 
best,  therefore,  for  the  activity  of  the  nitrifying  organisms. 

In  the  same  investigations,  it  was  found  that  the  con- 
centration of  the  soil  solution,  in  nitrates,  was  always 
greater  as  more  irrigation  water  was  used. 

In  view  of  the  tremendously  great  importance  of  soil 
life  in  the  maintenance  of  soil  fertility,  it  should  be  care- 
fully studied  under  the  conditions  of  irrigation. 

REFERENCES 

CAMERON,  F.  K.  The  Soil  Solution.  Chemical  Publishing  Company, 

Easton,  Pa.  (1911). 
CAMERON,  F.  K.,  and  GALLAGHER,  F.  E.    Moisture  Content  and 

Physical  Condition  of  Soils.     United  States  Department  of 

Agriculture,  Bureau  of  Soils,  Bulletin  No.  50  (1908). 
CAMERON,  F.  K.,  and  BELL,  JAMES  M.    The  Mineral  Constituents 

of  the  Soil  Solution.    United  States  Department  of  Agriculture, 

Bureau  of  Soils,  Bulletin  No.  30  (1905). 
CLARKE,  F.  W.  The  Data  of  Geochemistry.   Second  edition.  United 

States  Geological  Survey,  Bulletin  No.  491  (1911). 
COLLINS,  W.  D.    The  Quality  of  the  Surface  Waters  of  Illinois. 

United  States  Geological  Survey,   Water  Supply  Paper  No. 

239  (1910). 
CUSHMAN,  A.  S.    The  Effect  of  Water  on  Rock  Powders.    United 

States    Department    of    Agriculture,    Bureau    of    Chemistry, 

Bulletin  No.  92  (1905). 
DOLE,  R.  B.    Analyses  of  Waters  East  of  the  100th  Meridian. 

United  States  Geological  Survey,  Water  Supply  Paper  No.  236 

(1909). 


SOIL  CHANGES  DUE  TO  IRRIGATION  107 

FORBES,  R.  H.    The  River  Irrigating  Waters  of  Arizona.    Arizona 

Experiment  Station,  Bulletin  No.  44  (1902). 
FORBES,  R.  H.   Irrigating  Sediments  and  Their  Effects  Upon%Crops. 

Arizona  Experiment  Station,  Bulletin  No.  53  (1906). 
HARE,  R.  F.,  and  MITCHELL,  S.  R.    Composition  of  Some  New 

Mexico  Waters.     New  Mexico  Experiment  Station,   Bulletin 

No.  83  (1912). 
HILGARD,  E.  W.    Soils.    Chapters  VII  and  XVIII  (pp.  327-333). 

The  Macmillan  Company  (1906). 
KING,  F.  H.    Investigations  in  Soil  Management.    United  States 

Department  of  Agriculture,  Bureau  of  Soils,  Bulletin  No.  25 

(1905). 
KING,  F.  H.    Investigations  in  Soil  Management.    Madison,  Wis. 

(1904). 

PATTEN,  H.  E.    Heat  Transference  in  Soils.    United  States  Depart- 
ment of  Agriculture,  Bureau  of  Soils,  Bulletin  No.  59  (1909). 
STABLER,  HERMAN.    Some  Stream  Waters  of  the  Western  United 

States.    United  States  Geological  Survey,  Water  Supply  Paper 

No.  274  (1911). 
STEWART,  ROBERT,  and  GREAVES,  J.  E.    Study  of  the  Production 

and  Movement  of  Nitric  Nitrogen  in  an  Irrigated  Soil.    Utah 

Experiment  Station,  Bulletin  No.  106  (1909). 

STEWART,  ROBERT,  and  GREAVES,  J.  E.  Production  and  Movement 
of  Nitric  Nitrogen  in  Soil.   Centralblatt  fur  Bakteriologie, 
Band  34,  p.  115  (1912). 
WIDTSOE,  J.  A.,  and  STEWART,  ROBERT.    The  Dry-Farm  Soils  of 

Utah.   Utah  Experiment  Station,  Bulletin  No.  122  (1913). 
WINKLE,  W.  VAN,  and  EATON,  F.  M.    The  Quality  of  the  Surface 

Waters  of  California.    United  States  Geological  Survey,  Water 

Supply  Paper  No.  237  (1910). 


CHAPTER  VI 

CONDITIONS  DETERMINING  THE  USE  OF  SOIL 
MOISTURE  BY  PLANTS 

THE  discussion  in  the  preceding  chapters  has  taken 
no  account  of  the  effect  on  plants  of  soil  moisture.  Yet, 
the  plant  is  a  most  important  factor,  for  it  uses  immense 
quantities  of  water  throughout  the  season,  and  the  rate 
of  use  is  very  difficult  to  control.  It  becomes  necessary, 
therefore,  to  investigate  the  relationship  of  the  plant  to 
the  water  added  to  the  soil  in  irrigation.  The  relation- 
ship is  of  particular  importance,  because,  under  irriga- 
tion, the  farmer  may  apply  different  quantities  of  water, 
at  stated  times,  throughout  the  growing  season.  That  is, 
under  irrigation  a  soil-moisture  control  is  possible,  which 
is  not  possessed  by  any  other  system  of  agriculture. 

The  essential  question  in  agriculture  is  always,  "To 
what  extent  can  the  farmer  control  the  conditions  of 
plant-production?"  Where  water  is  the  critical  factor, 
as  in  irrigation,  it  is  of  first  importance  to  know  how  the 
absorption  of  water  from  the  soil  by  plants  may  be  con- 
trolled. Once  this  is  known,  systems  of  farming  may  be 
planned  whereby  the  scanty  water  supply  may  be  made  to 
reclaim  the  largest  possible  area  of  land,  or  to  produce 
the  largest  yield  of  high-quality  crops. 

This  chapter  is  devoted  to  a  discussion  of  the  condi- 
tions that  determine  the  rate  at  which  water  is  taken 
from  the  soil  by  plants.  The  rate  at  which  water  is  used  is 
ordinarily  different  from  the  total  quantity  used  by  the 

(108) 


USE  OF  SOIL  MOISTURE  BY  PLANTS  109 

plant  throughout  the  season.  A  rapidly  growing  plant, 
for  example,  may  use  daily  a  very  large  quantity  of.  water 
but  only  for  a  relatively  short  time,  while  a  more  slowly 
growing  plant,  using  daily  a  smal  er  quantity  of  water, 
but  for  a  longer  period  of  time,  may  in  the  end  use  much 
more  water.  The  rate  at  which  a  plant  uses  water  refers 
invariably  to  the  quantity  used  per  hour,  day  or  any  other 
unit  of  time,  during  certain  periods  of  its  growth,  and  is 
not  invariably  a  measure  of  the  total  water-needs  of  the 
crop. 

77.  Absorption  of  water  by  roots. — The  roots  are  the 
organs  of  water-absorption.  Practically  no  water  is  taken 
into  the  plants  by  the  stems  or  leaves  even  under  con- 
ditions of  heavy  rainfall.  In  the  absorption  of  water 
from  the  soil,  the  young  roots  are  most  active,  and,  of 
these,  only  certain  parts  are  actively  engaged  in  water- 
absorption.  At  the  tips  of  the  young  roots  are  numerous 
fine  hairs,  known  as  root-hairs,  clustering  near  the  tip  of 
the  root.  These  are  the  organs  of  the  plant  that  absorb 
soil  water.  As  the  root-hairs  grow  older,  they  lose  their 
power  of  water-absorption;  in  fact,  they  are  active  only 
when  they  are  in  actual  process  of  growth.  Water-absorp- 
tion, therefore,  occurs  near  the  tips  of  the  growing  roots, 
and,  whenever  the  plant  ceases  to  grow,  water-absorption 
also  ceases. 

The  root-hairs  are  filled  with  a  solution  of  various 
substances,  as  yet  poorly  understood,  which  play  an 
important  part  in  the  absorption  from  the  soil  of  water 
and  plant-food.  Owing  to  their  minuteness,  the  root- 
hairs  are  in  most  cases  immersed  in  the  moisture  film  that 
surrounds  the  soil  particles,  and  the  soil  moisture  is  taken 
directly  into  the  roots  from  this  film  by  the  process  of 
osmosis.  Without  entering  into  a  discussion  of  the  com- 


110  IRRIGA T10N  PRACTICE 

plicated  movement  of  water  from  the  soil  into  the  plant, 
it  may  be  said  that  the  concentration  of  the  solution  in 
the  root-hairs  is  higher  than  that  of  the  soil-water  solu- 
tion. The  water  tends,  therefore,  to  move  from  the  soil 
into  the  roots  to  make  the  solutions  inside  and  outside 
of  the  roots  of  the  same  concentration.  If  it  should 
occur  that  the  solutions  inside  and  outside  the  root-hairs 
were  of  the  same  concentration,  that  is  to  say,  if  they 
contained  the  same  substances  in  the  same  proportional 
amounts,  there  would  be  no  further  inward  movement  of 
water.  Moreover,  if  the  soil  moisture  should  become 
stronger  than  the  water  within  the  root-hairs,  water 
would  tend  to  pass  from  the  plant  into  the  soil.  This  is 
the  condition  that  prevails  in  the  alkali  lands  of  the 
West,  and  is  often  the  cause  of  the  death  of  plants  grow- 
ing on  such  lands. 

78.  Transpiration. — There  is  a  constant  movement  of 
water,  holding  in  solution  the  indispensable  plant  nutri- 
ents, after  it  has  entered  the  root-hairs,  through  the  roots, 
stems  and  into  the  leaves.  At  the  leaf  surfaces  evapora- 
tion occurs,  and,  there,  much  of  the  water  taken  from  the 
soil  passes  into  the  air  as  invisible  water  vapor.  The 
rapidity  of  this  current  is  often  considerable.  Ordinarily 
it  varies  from  1  to  6  feet  an  hour,  although  observations 
on  record  show  that  the  movement  often  reaches  the  rate 
of  18  feet  an  hour.  In  an  actively  growing  plant  it  does 
not  then  take  long  for  the  water  in  the  soil  to  find  its  way 
to  the  uppermost  parts  of  the  plant  and  to  be  evaporated 
from  the  leaf  surfaces.  This  movement  of  water  from  the 
soil,  through  the  plant,  into  the  air,  is  the  process  known 
as  transpiration.  If  the  current  of  water  passing  through 
the  plant  is  stopped  for  any  considerable  length  of  time, 
the  plant  is  injured  and  death  often  results.  Transpira- 


USE  OF  SOIL  MOISTURE  BY  PLANTS 


111 


tion  appears  to  be  a  process  wholly  necessary  to  plant  life. 
Our  question  is,  To  what  extent  may  it  be  reduced  with- 
out injuring  plant-growth? 

79.  The  initial  percentage  of  soil  moisture. — The 
most  important  factor  in  determining  the  rate  of  loss  of 
soil  water  is  the  average  percentage  of  water  found  in 
the  soil  at  the  beginning,  known  as  the  initial  percentage. 
All  other  conditions  being  the  same,  the  loss  of  water 
from  two  plants  during  a  definite  period  of  time  varies 
as  the  initial  percentage.  The  following  table,  selected 
from  a  great  number  of  experiments  on  this  subject 
made  at  the  Utah  Station,  illustrates  the  law: 


Length  of  period 

Average  per  cent 
of  water  at 
beginning 

Pounds  of  water 
lost  per 
square  foot 

Ten  days  

21.84 

25.05 

Ten  days  

13.18 

10.51 

Difference    

8.66  " 

14.54 

The  soil  which  contained  at  the  beginning  of  the 
experiment  21.84  per  cent  of  water,  lost  during  ten  days 
more  than  twenty-five  pounds  of  water  to  the  square  foot; 
whereas  the  soil  that  contained  13.18  per  cent  of  water  at 
the  beginning  of  the  period  lost  only  about  ten  and  one- 
half  pounds  of  water  to  the  square  foot.  It  seems  very 
clear  that  the  rate  of  loss  of  water  from  a  soil  increases  as 
the  initial  percentage  of  water  in  the  soil  increases;  that 
is,  the  higher  the  initial  percentage  of  water,  the  greater 
the  loss;  the  lower  the  initial  percentage,  the  smaller  the 
loss. 

The  reason  for  this  effect  of  the  initial  percentage  can 
be  fairly  well  understood.  The  fine  root-hairs  come  into 


112  IRRIGATION  PRACTICE 

contact  with  a  comparatively  small  area  of  the  soil-water 
film.  As  water  is  drawn  into  the  plant,  there  must  be  a 
flow  of  water  toward  the  point  of  contact  between  the 
active  roots  and  the  soil-moisture  film.  If  the  film  is 
thick,  the  water  will  move  with  some  freedom  and  the 
plant,  in  a  given  time  and  with  the  expenditure  of  a  given 
amount  of  energy,  will  absorb  a  larger  quantity  of  water 
than  would  be  possible  if  the  film  were  thin  and  offered 
greater  resistance  to  the  moving  water.  The  same  prin- 
ciple has  been  shown  to  hold  generally,  as  when  water 
evaporates  directly  from  the  surface  of  the  soil.  The  per- 
centage of  water  in  the  soil  is  a  fair  measure  of  the  thick- 
ness of  the  soil-water  film,  and  the  rate  of  loss  of  water 
from  the  soil  increases,  therefore,  as  the  initial  percentage 
of  moisture  in  the  soil  increases.  This  is  the  same  as  saying 
that  the  more  water  contained  by  the  soil  to  a  given  depth, 
the  more  is  lost  in  a  given  time  by  plant-  and  sun-action. 
This  important  law  seems  to  imply  that  plants  are  not 
able  to  regulate  the  quantity  of  water  taken  up  by  roots; 
but  rather  that,  assuming  all  other  factors  to  be  uniform, 
the  rate  of  transpiration  varies  only  with  the  ease  with 
which  water  may  be  obtained.  If  this  be  true,  plants 
may  easily  waste  water  if  too  much  is  found  in  the  zone 
of  root-growth;  unless,  indeed,  the  rate  of  growth  is 
proportional  to  the  use  of  water — a  condition  which  does 
not  exist.  Here  is  evidently,  then,  because  of  the  inability 
of  the  plant  to  regulate  its  consumption  of  soil  moisture,  a 
danger  which  the  farmer  must  carefully  heed.  While  the 
plant  cannot  possibly  be  prevented  from  taking  more 
water  from  moist  than  from  dry  soils,  yet,  the  farmer 
may  so  reduce  the  percentage  of  soil  moisture  that  the 
plant  is  not  always  absorbing  water  at  its  maximum 
capacity.  Manifestly,  in  spite  of  all  that  can  be  done. 


USE  OF  SOIL  MOISTURE  BY  PLANTS  113 

immediately  after  an  irrigation,  when  the  soil  is  moist, 
the  plant  will  of  necessity  use  much  more  moisture  per 
unit  of  time  than  later  when  the  soil  is  not  so  moist. 

A  question  of  importance  in  this  connection  is  this: 
If  two  fields  contain  respectively  20  per  cent  and  10  per 
cent  of  water,  will  the  loss  of  soil  moisture  during  any 
definite  period  be  twice  as  great  from  the  one  field  as 
from  the  other?  From  the  data  in  our  possession,  it 
may  be  answered  that  the  losses  are  proportionally 
larger  from  the  wettest  soils.  This  may  be  seen  from  the 
table  on  page  111.  The  difference  in  the  moisture  per 
cent  is  only  8.66  but  the  difference  in  the  pounds  of 
water  lost  to  the  square  foot  during  the  same  period  was 
14.54.  That  is  to  say,  the  wetter  the  soil  became,  the 
more  rapid  did  the  proportional  loss  of  moisture  become. 
This  important  phase  of  the  law  of  the  initial  percentage 
might  have  been  foretold  by  recalling  that  the  thinner  the 
soil-moisture  film,  the  more  firmly  is  it  held  by  the  soil. 
Under  the  point  of  lento-capillarity,  plants  can  absorb  the 
soil  moisture  only  with  the  greatest  difficulty;  above  this 
point,  the  absorption  goes  on  much  more  rapidly.  Pre- 
liminary experiments  seem  to  show  that,  if  the  lento-cap- 
illary water  of  a  soil  be  subtracted  from  the  percentage 
of  water  held  by  each  of  two  or  more  soils,  and  the  cube 
roots  be  taken  of  the  remainders,  that  is,  of  the  water  in 
true  capillary  condition,  an  approximately  correct  meas- 
ure of  the  relative  ease  with  which  plants  can  abstract 
water  from  the  soil  is  obtained. 

The  law  of  the  initial  percentage  teaches  the  impor- 
tant doctrine  that  moderate  irrigations  are  in  all  proba- 
bility more  economical  than  heavy  ones;  and  it  may 
explain  why  heavy  irrigations,  as  will  be  shown  later,  do 
not  yield  proportional  increases  of  dry  matter, 
H 


114 


IRRIGATION  PRACTICE 


80.  Distribution  of  water  in  the  soil. — The  distribu- 
tion of  water  in  the  soil  is  likewise  important  in  determi- 
ning the  rate  at  which  plants  use  water. 


Length  of  period 

Per  cent 
of  water  in 
first  foot 

Average  per  cent 
of  water  to 
depth  of  8  feet 

Pounds  of  water 
lost  per 
square  foot 

Ten  days    .... 
Ten  days    .... 

Difference  .    .    . 

23.68 
17.25 

17.69 
16.85 

18.24 
13.55 

6.43 

0.84 

4.69 

As  shown  in  the  above  table,  two  soils  may  each  con- 
tain approximately  an  average  of  17  per  cent  of  water  to 
a  depth  of  8  feet,  but  in  the  first  the  percentage  of  mois- 
ture in  the  first  foot  is  over  23  per  cent,  while  in  the  second 
the  percentage  of  moisture  in  the  first  foot  is  about  17 
per  cent.  That  is,  the  distribution  of  water  is  not  the 
same  in  the  two  soils.  In  such  a  case,  more  water  is  lost 
from  the  soil  in  which  the  water  is  heaped  up  near  the 
surface.  The  more  evenly  the  water  is  distributed  to 
the  full  depth  of  root-action,  the  more  slowly  does  the 
plant  consume  the  water  during  any  given  period  of  time. 
The  data  in  the  table  show  that  during  a  period  of  ten 
days,  where  the  top  soil  was  wettest,  4.69  pounds  more 
were  lost  to  the  square  foot  than  where  the  water  was 
more  evenly  distributed  throughout  the  soil. 

The  greater  water  loss  from  soils,  otherwise  alike,  that 
contain  a  large  proportion  of  water  in  the  first  foot,  may 
be  explained  in  part  by  the  greater  root-development  in 
the  upper  layers  of  the  soil.  Roots  are  well  developed  in 
arid  soils  to  a  depth  of  10  or  more  feet,  but  the  larger  part 
of  the  small  roots  are  developed  within  the  upper  3  or  4 
feet.  Moreover,  when  the  top  soil  is  abundantly  rich  in 


USE  OF  SOIL  MOISTURE  BY  PLANTS  115 

water,  direct  evaporation  from  the  soil  occurs  much  more 
freely. 

To  prevent  the  accumulation  of  water  in  the  upper 
foot,  and  the  consequently  greater  loss  of  soil  moisture, 
the  land  should  be  plowed  deeply,  so  that  the  irrigation 
water  may  move  easily  and  rapidly  to  the  lower  soil 
layers.  For  the  same  reason,  the  soil  should  be  kept 
moist  enough  to  permit  water  to  descend  quickly.  The 
limiting  of  root-development  in  the  upper  foot  by  deep 
cultivation  may  also  be  advantageous.  Whatever  device 
the  farmer  may  employ  to  distribute  water  uniformly  to 
comparatively  great  depths,  and  to  prevent  the  excessive 
development  of  roots  in  the  upper  soil  layers,  will  tend  to 
reduce  the  rate  at  which  plants  will  absorb  water  from 
the  soil.  Under  the  law  of  distribution,  as  explained  in 
Chapter  III,  the  proportion  of  water  is  normally  greater 
in  the  upper  than  in  the  lower  soil  layers;  yet,  by  proper 
cultural  treatments,  it  is  possible  to  effect  the  most  com- 
plete distribution  in  the  shortest  time,  and  thus  to  con- 
serve the  water. 

81.  The  effect  of  time. — Closely  connected  with  the 
law  of  the  initial  percentage,  and  derived  from  it,  is  the 
further  law  that  as  time  goes  on,  the  rate  of  loss  of  soil 
moisture  becomes  smaller  and  smaller.  In  the  beginning, 
when  the  soil  is  moist,  much  water  is  lost.  After  the  first 
day,  there  is  a  smaller  quantity  of  water  in  the  soil,  and 
the  rate  of  loss  will  be  a  trifle  smaller,  and  so  on,  day  after 
day,  until  a  period  is  reached  which  finds  the  soil  so  dry 
that  the  plant  can  no  longer  draw  water  from  it.  On  a 
shallow  soil,  during  two  weeks  after  irrigation,  more  than 
31  per  cent,  or  nearly  one-third,  of  the  total  loss  of  water 
occurred  during  the  first  three  days  after  irrigation;  29 
per  cent  the  next  four  days;  23  per  cent  the  next  three 


116  IRRIGATION  PRACTICE 

days;  and  17  per  cent  the  last  four  days  of  the  two-week 
period.  Similar  proportional  figures  were  found  for 
longer  periods.  On  a  deep  soil,  of  good  water-holding 
power,  during  fourteen  days  after  irrigation,  62  per  cent 
of  the  total  loss  occurred  during  the  first  seven  days,  and 
only  38  per  cent  during  the  second  week.  Such  figures, 
which  might  be  multiplied  by  drawing  from  many  experi- 
ments on  the  subject,  show  that  methods  designed  to 
conserve  soil  moisture  should  be  put  into  operation  as 
soon  as  possible  after  irrigation.  Especially  to  prevent 
direct  evaporation,  the  soil  should  be  cultivated  as  soon 
as  possible  after  irrigation — in  fact,  as  soon  as  the  soil  is 
dry  enough  to  support  the  cultivator  without  injuring  the 
structure  of  the  soil. 

82.  The  depth  of  soil. — The  deeper  the  soil,  the  aver- 
age percentage  of  soil  moisture  being  the  same,  the  larger 
is  the  loss  of  water  in  a  given  period  of  time.  This  law  is 
easily  understood.  If  two  soils  weighing  100  pounds  to 
the  cubic  foot  are  1  and  2  feet  deep  respectively,  and  both 
contain  an  average  of  20  per  cent  of  moisture,  they  will 
contain  respectively  to  the  square  foot  of  surface,  and  to 
their  full  depth,  twenty  and  forty  pounds  of  water.  Dur- 
ing the  first  day,  each  soil  will  lose,  say,  two  pounds  of 
water.  There  will  remain,  at  the  beginning  of  the  second 
day,  in  the  shallow  soil,  eighteen  pounds,  and  in  the  deep 
soil,  thirty-eight  pounds  of  water,  or  18  per  cent  and  19 
per  cent — the  deeper  soil  having  a  higher  percentage  of 
moisture.  During  the  second  day,  then,  in  accordance  with 
the  law  of  the  initial  percentage,  the  deeper  soil  will  lose 
more  water  than  will  the  shallow  soil.  The  difference 
will  become  more  marked  with  each  passing  day.  Other 
factors  enter  in,  as  the  fuller  development  of  plant  roots 
in  deep  soil,  but,  assuming  all  other  factors  to  be  the  same, 


USE  OF  SOIL  MOISTURE  BY  PLANTS  117 

the  deeper  the  soil  the  more  rapidly  will  the  soil  lose  its 
moisture.  It  does  not  follow  from  this  law  that  the  deep 
soil  will  dry  out  more  rapidly  than  a  shallow  one.  On  the 
contrary,  since,  in  the  case  above  suggested,  there  is  only 
half  as  much  water  in  the  shallow  soil  as  in  the  deep  soil, 
the  shallow  soil,  with  a  smaller  rate  of  loss,  will  dry  out 
very  much  more  quickly  than  will  the  deep  soil  with  a 
larger  rate  of  loss.  This  must  be  understood  and  remem- 
bered by  the  farmer  who  is  dealing  with  shallow  soils. 

Various  kinds  of  shallow  soils  occur  in  the  irrigated 
district.  In  some  cases  a  hardpan  has  been  formed  a  few 
feet  below  the  surface,  which  does  not  readily  disintegrate 
under  the  influence  of  irrigation.  This  leaves  a  compara- 
tively shallow  soil  in  which  to  store  moisture,  which  dries 
out  quickly  and  must  be  irrigated  frequently.  Many  soils 
are  underlaid  at  a  depth  of  a  few  feet  with  coarse,  loose 
gravel,  through  which  water  percolates  and  is  lost.  Such 
shallow  soils  must  be  treated  as  are  soils  with  hardpan 
near  the  surface.  However,  where  an  impervious  hardpan 
underlays  the  soil,  if  too  much  water  be  applied,  there  is 
greater  danger  of  water-logging;  whereas,  on  soils  under- 
laid with  loose  gravel  there  is  little  such  danger,  for  the 
excess  moisture  percolates  downward  and  is  lost.  From 
another  point  of  view,  also,  this  is  important.  On  shallow 
soils  of  any  kind,  a  given  quantity  of  water  cannot  dis- 
tribute itself  over  considerable  depths.  As  a  consequence, 
the  percentage  of  soil  moisture  is  higher,  which  causes  a 
more  rapid  loss  of  soil  moisture.  From  the  point  of  view 
of  the  conservation  of  soil  moisture,  such  soils  are,  there- 
fore, less  economical  than  deep  ones. 

83.  Physical  composition  of  soils. — The  rate  of  loss 
of  soil  moisture  from  cropped  fields  varies  with  the  physical 
composition  of  the  soil.  In  a  fine  soil,  a  given  quantity  of 


118  IRRIGATION  PRACTICE 

water  will  be  spread  over  a  much  larger  surface  of  soil 
particles  and  the  film,  therefore,  will  be  thinner;  hence,  the 
water  will  be  absorbed  at  a  slower  rate  than  from  a  coarse- 
grained soil,  which  exposes  a  smaller  surface  and  over 
which  the  same  quantity  of  water  forms  a  much  thicker 
film.  It  may  be  demonstrated  that,  with  a  given  quantity 
of  water,  the  thickness  of  the  film  that  forms  over  soil 
particles  varies  as  the  radius  of  the  soil  grains.  That  is, 
if  in  a  given  soil  the  particles  are  twice  as  large  in  diame- 
ter as  in  another,  a  given  quantity  of  water  added  to 
these  soils  will  form  a  film  twice  as  thick  in  the  coarse 
soil  as  in  the  fine  one.  Consequently,  plants  growing  on 
fine-grained  soils  will  use  water  at  a  lower  rate  than 
those  growing  on  coarse-grained  soils.  In  other  words, 
under  conditions  otherwise  uniform,  the  more  clay  a 
soil  contains  the  less  rapidly  does  the  plant  draw  water 
from  it. 

84.  Chemical  composition  of  soils. — The  chemical 
composition  of  the  soil  also  determines  the  rate  at  which 
plants  take  moisture  from  the  soil.  This  factor  is  of 
especial  importance  because  it  is  within  the  power  of  the 
farmer  to  change,  at  least  in  a  small  way,  the  chemical 
composition  of  the  soil,  by  proper  methods  of  tillage,  or  by 
the  direct  addition  to  the  soil  of  manure  or  commercial 
fertilizers.  As  explained  in  Chapter  V,  the  chemical  sub- 
stances of  which  the  soil  is  composed  are  gradually  dis- 
solved by  the  soil  moisture.  The  soil  solution  of  different 
soils  varies,  therefore,  with  the  composition  of  the  soil 
and  the  quantity  of  water  added.  The  root-hairs,  through 
which  soil  moisture  is  absorbed,  lie  immersed  in  the  soil 
solution.  The  rate  at  which  water  is  taken  from  the  soil 
by  these  plant  roots  depends  largely  upon  the  relative 
strength  of  the  solution  inside  and  outside  of  the  root- 


USE  OF  SOIL  MOISTURE  BY  PLANTS  119 

hairs.  In  general,  the  stronger  the  soil  solution  the  less 
rapidly  will  plants  take  water  from  the  soil  with  a  given 
rate  of  growth.  This  is  not  an  invariable  law,  however, 
since  it  depends,  in  part,  on  the  nature  of  the  soil  materials 
that  go  into  solution.  If  the  soil  solution  is  acid,  the  rate 
of  absorption  by  plants  is  accelerated;  if  alkaline,  it  is 
retarded.  In  the  vast  majority  of  cases,  soils  are  alkaline 
rather  than  acid.  Especially  in  arid  regions  is  the  occur- 
rence of  acid  soils  infrequent. 

The  soil  solutions  of  fertile  soils  are  usually  more  con- 
centrated than  those  of  less  fertile  soils.  It  follows,  there- 
fore that,  the  more  fertile  a  soil  is,  the  less  rapidly  does  the 
plant  absorb  the  soil  moisture  with  a  given  rate  of  growth. 
This  law,  which  has  been  demonstrated  in  a  number  of 
interesting  experiments,  teaches  the  farmer  the  great 
importance  of  keeping  the  soil  in  a  most  fertile  condition. 
Bouyoucos  has  made  some  interesting  observations  on 
this  subject.  As  above  stated,  the  more  concentrated  the 
soil  solution  is,  the  less  rapidly  do  plants  take  moisture 
from  the  soil.  Yet  this  concentration  need  not  always  be 
due  to  plant-food,  for  Bouyoucos  has  shown  that  an 
innocuous  soluble  substance,  such  as  common  salt  or 
sodium  sulfate,  if  added  to  the  soil,  decreases  the  rate 
at  which  the  plants  take  water  from  the  soil.  This  is 
important  because  of  the  fact  that  in  a  great  many 
irrigated  soils  of  the  country,  resulting  from  the  peculiar 
climatic  conditions,  are  found  considerable  quantities  of 
common  salt,  and  soluble  salts  of  magnesium,  calcium 
and  other  elements  which  are  not  needed  as  plant-foods. 
These  accumulations,  ordinarily  known  as  alkali,  when 
present  in  large  quantities,  are  a  serious  menace  to  suc- 
cessful agriculture.  The  above  law  seems  to  show,  how- 
ever, that  the  presence  of  such  materials  in  the  soil  may 


120  IRRIGATION  PRACTICE 

be  of  distinct  value  in  diminishing  the  rate  of  loss  of 
water  from  the  soil.  Consequently  it  follows,  also,  that 
on  alkali  soils  the  rate  at  which  water  is  transpired  is 
smaller  than  on  soils  that  are  free  from  alkali.  This 
may,  in  a  small  measure,  account  for  the  fact  that  even 
cropped  alkali  lands  remain  rather  moist  throughout  the 
season. 

If  all  this  be  true,  however,  it  is  within  the  power  of 
the  farmer  so  to  maintain  the  soluble  material  in  the 
soil  as  to  permit  the  plant  to  draw  water  from  the  soil 
at  the  slowest  possible  rate.  By  proper  methods  of 
cultivation  whereby  plant-food  is  set  free,  by  the  appli- 
cation of  commercial  fertilizers,  of  manure,  or  by  innocu- 
ous salts,  such  as  the  abundant  sodium  sulfate,  it  is 
possible  to  maintain  the  soil  solution  in  a  high  degree  of 
concentration  and  thereby  secure  for  the  plant  the  neces- 
sary foods  at  a  very  slow  rate.  This  fundamentally  impor- 
tant factor  in  the  economical  use  of  water  by  plants,  has 
received  in  the  past  practically  no  attention,  but  is  now 
becoming  more  generally  recognized. 

85.  Plowing.-^ Among  the  cultural  processes  that  have 
for  their  purpose  the  reduction  of  the  rate  of  loss  of  water 
from  the  soil,  none  is  more  important  than  the  ancient 
art  of  plowing,  which  is  the  fundamental  practice  in  all 
agriculture.  From  the  point  of  view  of  the  irrigation 
farmer,  and  the  saving  of  soil  moisture,  plowing  has  dis- 
tinct advantages.  First,  it  permits  the  easier  descent  of 
water  into  the  soil  and  consequently  a  more  rapid  and  more 
uniform  distribution  throughout  the  soil.  This  results 
in  a  smaller  rate  of  loss.  Second,  thorough  and  careful 
plowing  at  the  right  time  of  the  year,  preferably  in  the 
fall,  gives  every  soil  activity  new  freedom,  thereby  releas- 
ing more  plant-food  and  rendering  the  soil  solution  more 


USE  OF  SOIL  MOISTURE  BY  PLANTS  121 

concentrated.    Thorough  and  careful  plowing  results  in  a 
diminished  rate  of  loss  of  water  from  cropped  soils. 

86.  Cultivation. — The  frequent  cultivation  of  the  soil, 
as  discussed  in  Chapter  III,  has  for  its  purpose  the  reduc- 
tion of  the  direct  evaporation  of  water  from  the  soil. 
It  has,  however,  a  number  of  other  beneficial  effects  of 
high  importance  to  the  irrigation  farmer.    For  example, 
cultivation  diminishes  the  rate  at  which  plants  take  water 
from  the  soil,  and  further,  as  will  be  shown  later,  it  even 
diminishes  the  quantity  of  water  required  to  produce  a 
given  quantity  of  dry  matter.     Cultivation  is  essential 
in  irrigation  agriculture  because  it  diminishes  the  direct 
evaporation  from  the  soil  and  because  it  reduces  the 
quantity  of  water  transpired  by  plants.    It  is  a  practice 
that  should  be  observed  faithfully  by  the  farmer  through- 
out the  season.    After  every  rainfall  and  after  every  irri- 
gation, just  as  far  as  possible  from  spring  until  fall,  the 
soil  should  be  carefully  stirred  by  the  farmer.    The  cost 
of  such  treatment  will  be  more  than  paid  for  in  the  greater 
yields  of  crops,  and  hi  the  greater  producing  power  of 
water. 

87.  Manuring. — It  is  quite  evident,  from  what  has 
been  said  already,  that  manuring,  or  the  adding  to  the 
soil  of  plant-foods,  under  a  given  rate  of  growth  will  tend 
to  reduce  evaporation.   This  is  another  argument  in  behalf 
of  manuring — a  practice  which,  unfortunately,  has  not 
been   carefully   observed   by   the    irrigation   farmers   of 
America.     As   time  goes  on  and  water  becomes  more 
precious,  and  the  population  of  the  arid  region  increases, 
the  art  of  manuring,  whether  with  natural  or  artificial 
fertilizers,  will  acquire  a  greater  and  greater  importance. 

88.  Vigor  of  plant. — The  rate  of  loss  of  soil  moisture 
due  to  plants  depends  very  largely  upon  the  vigor  of  the 


122  IRRIGATION  PRACTICE 

plant  itself.  A  sickly  plant  evidently  does  not  require,  nor 
can  it  use,  so  large  quantities  of  water  as  a  strong,  healthy 
plant.  Many  farmers  fail  to  understand  this  simple  and 
almost  self-evident  law,  and  therefore  apply  to  a  crop 
poorly  developed  fully  as  much  water  as  is  applied  to 
one  which  is  growing  vigorously. 

89.  Root-system. — Another  factor  of  importance  in 
determining  the  rate  of  loss  of  soil  water  due  to  plants  is 
the  development  of  the  root-system.    If  the  roots  have 
been  developed  near  the  surface,  more  water  will  be  used 
from  the  top  soil  than  if  the  roots  have  been  more  evenly 
distributed  throughout  the  soil,  and  the  energy  expended 
in  lifting  the  water  from  the  lower  depths  is  increased. 
To  drive  the  roots  downward,  water  should  not  be  applied 
too  early  in  the  season,  nor  should  it  be  applied  in  such 
quantities  as  to  make  it  unnecessary  for  the  lower  roots 
to  continue  their  work.    Only  when  the  roots  fill  the  soil 
to  the  greatest  depth  in  the  most  thorough  manner,  will 
the  soil  moisture  be  used  most  economically. 

90.  Age   of   plants. — The   age   of   a   plant   naturally 
determines,  largely,  the  rate  at  which  soil  moisture  is 
absorbed.    A  plant  increases  very  rapidly  in  dry  weight, 
up  to  the  time  of  flowering.   After  this  time  the  increase 
is  slight,  and  finally  diminishes.   The  rate  at  which  plants 
use  water  varies  somewhat  in  the  same  way.    There  is  a 
steady  increase  in  the  rate  at  which  plants  use  water 
from  early  spring  up  to  flowering;  after  which  there  is 
a  diminution,  until,  when  the  plant  is  old,  it  uses  water 
at  a  very  low  rate.    A  similar  relation  exists  between 
growth  and  water-use  of  biennial  crops  such  as  sugar 
beets.   The  effect  of  the  age  of  plants  on  the  rate  of  loss 
of  soil  water  is  well  shown  in  the  following  table: 


USE  OF  SOIL  MOISTURE  BY  PLANTS 


123 


POUNDS  OF  WATER  LOST  DAILY  PER  SQUARE  FOOT 
(Rate  increases  to  flowering,  then  decreases.) 


Crop 

July 

August 

September 

Corn            

2.06 

2.46 

2.07 

Sugar  beets    

1.33 

1.53 

1.04 

Wheat     

1.29 

0.95 

It  is  to  be  remembered  that,  in  this  table,  the  initial 
percentages  are  not  in  all  cases  the  same,  so  that  the  dif- 
ferent crops  cannot  be  compared  as  to  their  power  to 
abstract  water.  The  only  legitimate  use  of  the  table  is  to 
compare  the  quantities  of  water  for  each  crop  that  were 
lost  in  July,  August  and  September — the  months  of  the 
growing  season.  In  the  case  of  corn,  the  greatest  loss  came 
in  August;  while  in  July  and  September,  the  loss  was  prac- 
tically the  same.  In  the  case  of  sugar  beets,  the  greatest 
loss  also  came  in  August;  the  next  in  July,  and  the  smallest 
in  September.  In  the  case  of  wheat,  the  largest  loss  came 
in  July  and  the  smallest  in  August.  These  variations  are 
readily  explained  by  remembering  that,  under  the  climatic 
conditions  prevailing,  the  wheat  matured  in  July  and  was 
harvested  in  August,  thus  corresponding  with  the  rates 
of  loss  as  shown  above;  while  the  corn  and  sugar  beets 
continued  their  vigorous  growth  into  September.  The 
time  of  most  rapid  growth  is  usually  the  time  of  greatest 
daily  water  use. 

91.  The  kind  of  crop. — The  kind  of  crop  also  influences, 
materially,  the  rate  at  which  water  is  taken  from  the  soil. 
No  two  crops  appear  to  be  exactly  alike  in  their  power  to 
absorb  soil  moisture.  Much  work  is  yet  to  be  done  on 
this  subject  before  really  definite  results  can  be  given. 
Meanwhile,  some  general  laws  have  been  observed  which 
can  safely  be  stated,  at  least  until  further  knowledge  is 


124  IRRIGATION  PRACTICE 

gathered.  It  appears  that  crops  which  mature  early  use 
water  more  rapidly  than  those  which  have  a  longer  grow- 
ing period.  For  example,  under  the  conditions  prevailing 
in  the  irrigated  sections  of  the  United  States,  wheat  and 
oats  use  daily  more  water  than  corn,  beets  or  potatoes, 
although  in  the  aggregate,  wheat  and  oats  use  much  less 
water  than  do  the  longer-growing  crops.  Wheat,  oats 
and  similar  crops  hasten  on  to  maturity  and,  in  so  doing, 
use  water  at  a  very  rapid  rate.  Corn,  potatoes  and  sugar 
beets  continue  their  steady  growth  throughout  the  season, 
and  the  rate  at  which  they  use  water  is  considerably 
smaller.  Lucern,  which  is  cut  from  two  to  four  or  even 
more  times  during  the  season,  behaves  pretty  much  as  if 
it  were  a  series  of  quickly  growing  crops. 

The  rate  at  which  various  crops  use  water  may  be 
roughly  estimated  by  the  degree  to  which  soils  are  dried 
out  during  long  periods  without  irrigation  by  the  respec- 
tive crops.  Experiments  show  that,  from  this  point  of 
view,  lucern  comes  first,  followed,  in  order,  by  wheat, 
oats,  corn,  sugar  beets  and  potatoes.  This  is  practically 
the  order  obtained  in  direct  experimentation.  More 
information  is  needed  regarding  the  relative  powers  of 
different  crops  to  abstract  soil  moisture. 

92.  The  seasons. — The  farmer  may,  in  a  measure, 
control  most  of  the  factors  already  discussed,  but  Jie  is 
helpless  when  it  comes  to  controlling  the  varying  seasons. 
No  one  factor  is  so  powerful  in  influencing  crop-growth 
as  are  the  seasons,  and  with  this  factor  the  farmer  must 
always  reckon.  The  average  temperature  throughout 
the  season  is  of  first  importance  in  determining  plant- 
growth,  and  therefore,  in  a  large  measure,  the  rate  at 
which  the  plant  uses  water.  With  a  high  average  tempera- 
ture, plant-growth  is  rapid  and  the  daily  loss  of  soil 


USE  OF  SOIL  MOISTURE  BY  PLANTS  125 

moisture  is  great.  Sunshine  is  next  in  importance.  The 
more  abundant  the  sunshine  throughout  the  growing 
season,  the  more  favorably  affected  is  plant-growth,  and 
the  more  rapid  is  the  loss  of  the  soil  moisture.  Third  in 
importance  is  the  relative  humidity  of  the  air.  The  drier 
the  air,  the  more  rapidly  does  water  evaporate  from  the 
plant,  and,  therefore,  the  more  steadily  does  water  move 
through  the  plant  from  the  soil.  Following  these  three 
factors — temperature,  sunshine  and  humidity — are  winds 
and  all  manner  of  air  movements.  These  dry  out  the 
soil  and  increase  the  rate  at  which  water  passes  through 
the  plant  to  supply  the  more  rapid  evaporation  from  the 
plant.  Winds  are  always  a  serious  factor  of  water-loss, 
largely  beyond  the  control  of  the  farmer.  Rains,  especially 
slight  ones,  during  the  growing  season  are  a  menace,  for 
they  keep  the  top  soil  moist  and  make  possible  a  rapid 
direct  evaporation;  however,  they  tend  to  diminish  trans- 
piration, from  the  reduction  in  the  relative  humidity 
which  follows  them.  These  factors,  fundamental  in 
determining  the  season,  determine  largely  the  evaporation 
of  water  from  the  soil  itself.  Experiments  have  shown  that 
the  rate  of  loss  of  soil  moisture  due  to  plant-action  is 
frequently  varied  as  a  result  of  the  seasons. 

The  factors  of  water-loss  discussed  in  this  chapter 
are  those  of  most  importance  to  the  irrigation  farmer. 
Many  of  them  may  be  controlled  more  or  less  perfectly 
and,  therefore,  they  should  be  well  understood. 

REFERENCES 

BOUYOUCOS,  GEORGE  J.  Transpiration  of  Wheat  Seedlings  as 
Affected  by  Soils,  by  Solutions  of  Different  Densities,  and  by 
Various  Chemical  Compounds.  Proceedings  of  the  American 
Society  of  Agronomy,  Vol.  Ill,  pp.  130-191  (1911). 


126  IRRIGATION  PRACTICE 

BRIGGS,  LYMAN  J.,  and  SHAUTZ,  H.  L.  The  Water  Requirements  of 
Plants.  United  States  Department  of  Agriculture,  Bureau  of 
Plant  Industry,  Bulletins  Nos.  284  and  285  (1913). 

BUERGERSTEIN,  A.   Die  Transpiration  der  Pflanzen  (1904). 

WIDTSOE,  J.  A.,  and  MCLAUGHLIN,  W.  W.  The  Movement  of  Water 
in  Irrigated  Soils.  Utah  Experiment  Station,  Bulletin  No.  115 
(1912). 

WIDTSOE,  J.  A.  Factors  Influencing  Evaporation  and  Transpira- 
tion. Utah  Experiment  Station,  Bulletin  No.  105  (1909). 

UTAH  STATION  STAFF.  Irrigation  Investigations.  Utah  Experiment 
Station,  Bulletin  No.  80  (1902). 


CHAPTER  VII 
THE  WATER-COST  OF  DRY  MATTER 

THE  steady  transpiration  stream  of  water,  passing  from 
the  soil  through  all  growing  plants  to  be  evaporated  at  the 
leaves,  is  responsible  for  the  largest  loss  of  soil  moisture. 
This  loss  is,  also,  the  most  difficult  to  control;  for,  as 
shown  in  previous  chapters,  direct  evaporation  from  the 
soil  may  be  largely  prevented  by  simply  stirring  the  top 
soil,  but  many  complex  factors  are  involved  in  the  loss 
of  water  by  transpiration.  Many  experiments  have  been 
made  to  determine  the  relative  quantities  of  water  lost 
by  evaporation  and  transpiration.  While  no  absolute 
numbers  of  general  application  have  been  obtained,  yet, 
when  the  land  is  not  cultivated  to  prevent  evaporation, 
one  and  one-half  times  as  much  water  evaporates  ordi- 
narily from  the  vigorous,  growing  plant  as  from  the  soil. 
When  the  soil  is  well  tilled,  and  direct  evaporation  thus 
reduced,  the  water  lost  by  transpiration  is  often  five  to 
ten  times  greater  than  the  quantity  lost  by  evaporation 
from  the  corresponding  area  of  soil. 

This  great  loss  of  soil  moisture  by  transpiration  is  a 
matter  of  much  concern  to  the  farmer,  who  pursues  his 
work  in  the  hope  of  reaping  the  largest  harvest  from 
the  land,  water  and  labor  employed.  Especially,  where 
water  is  scarce  or  irrigation  is  practised,  the  important 
question  is  whether  the  increased  yield  is  in  proportion 
to  the  quantity  of  water  passing  through  the  crop  by 
transpiration.  If  the  yield  increases  in  proportion  to  the 

(127) 


128  IRRIGATION  PRACTICE 

increase  in  transpiration,  there  will  be  no  need  to  reduce 
transpiration.  If,  on  the  other  hand,  the  water-cost  of 
the  crop  is  partly  independent  of  the  transpiration  stream, 
it  may  become  necessary  to  decrease  or  increase  trans- 
piration to  a  point  at  which  the  largest  yield  of  dry  matter 
is  produced  with  the  smallest  quantity  of  water.  Only 
when  this  is  done  does  irrigation  give  its  greatest  returns. 

93.  Carbon  assimilation. — Practically  one-half  of  a 
plant  consists  of  the  element  carbon.  From  2  to  10  per 
cent  consists  of  mineral  matter,  taken  from  the  soil,  and 
brought  into  the  plant  in  the  process  of  transpiration. 
The  remainder  of  the  plant  consists  of  the  elements  of 
water  combined  with  carbon  and  mineral  matter  to  form 
the  variety  of  plant  constituents. 

The  carbon,  constituting  one-half  or  more  of  the  dry 
plant,  is  obtained  by  the  plant  from  the  air  through  leaf- 
action.  The  gas  carbon  dioxid  constitutes  about  three 
parts  in  10,000  parts  of  air.  As  the  air  washes  against 
the  leaves  of  plants,  this  gas  finds  its  way  into  the  leaves 
of  green  plants  through  small  openings,  known  as  stomata, 
or  breathing  pores,  which  occur  in  great  abundance, 
especially  on  the  lower  side  of  the  leaves.  The  stomata 
are  delicately  adjusted  valves  which  as  they  open  and  close 
are  entrances  to  relatively  large  open  spaces  within  the 
leaves  themselves.  When  the  carbon  dioxid  enters  the 
leaves  through  the  breathing  pores,  it  is  rapidly  absorbed 
by  the  juices  of  the  leaves  and  immediately  decomposed 
into  the  element  carbon  and  the  element  oxygen.  The 
oxygen  is  returned  to  the  atmosphere,  while  the  carbon 
is  retained  and  combined  with  water  and  other  substances 
with  the  formation  of  sugars,  starches  and  other  valuable 
plant  constituents.  This  process  of  carbon  assimilation 
continues  without  intermission  in  green  plants  during  the 


THE  WATER-COST  OF  DRY  MATTER  129 

time  of  bright  daylight  or  of  sunshine.  Chlorophyll,  the 
green  coloring  matter  of  higher  plants,  and  sunshine  are 
indispensable  for  this  wonderful  decomposition  and  new 
composition. 

A  simple  calculation  will  show  how  actively  the  leaves 
of  the  plant  must  be  at  work  decomposing  carbon  dioxid 
and  building  up  the  new  compounds  derived  from  the 
assimilated  carbon.  It  is  not  uncommon  in  the  irrigated 
section  that  an  acre  of  well-developed  lucern  yields,  in 
one  season,  10,000  pounds  of  dry  matter.  One-half,  or 
5,000  pounds,  of  this  crop  consists  of  the  element  carbon, 
obtained  from  the  gas  carbon  dioxid  of  the  air  by  the 
countless  leaves  that  have  swayed  back  and  forth  in  the 
air  throughout  the  growing  season.  Each  tiny  leaf  has 
done  but  a  small  part  of  the  work,  but  the  total  gives  a 
lively  appreciation  of  the  tremendous  activity  of  plant 
leaves. 

94.  Plant  age  and  carbon  assimilation. — The  rate  at 
which  this  assimilation  of  carbon,  or  "growth,"  takes  place 
varies  wuth  the  maturity  of  the  plant.  To  illustrate,  at 
the  Utah  Station  careful  measurements  were  made  of  the 
total  acre  weight  of  dry  matter  in  a  crop  of  lucern  from 
May  4  to  August  24,  covering  practically  the  whole  of 
the  growing  season.  In  early  May,  when  the  plant  was 
well  established,  the  weekly  gain  of  dry  matter  was 
something  over  300  pounds  to  the  acre;  this  increased 
steadily  until  just  before  the  time  of  flowering,  when  it 
was  nearly  800  pounds,  after  which  it  gradually  decreased 
until  late  in  July,  when  there  was  a  loss  instead  of  gain. 
This  represents  a  general  law  of  plant-growth.  At  the 
beginning  of  the  growing  season  the  daily  or  weekly  gains 
of  the  crop  are  small,  but  they  increase  steadily  and  rather 
rapidly,  providing  the  conditions  of  growth  are  favorable, 


130  IRRIGATION  PRACTICE 

until  the  maximum  rate  of  increase  occurs  about  the  time 
of  flowering.  After  flowering,  as  seed-formation  sets  in, 
the  rate  of  growth  becomes  smaller,  for,  from  that  time 
on,  the  main  energies  of  the  plant  are  no  longer  directed 
to  the  increase  in  dry  matter,  but  concern  themselves 
more  largely  with  the  elaboration  of  the  food  materials 
already  gathered  into  seed  to  be  used  for  the  perpetuation 
of  the  species. 

Evidently,  since  water  is  unquestionably  necessary  in 
plant-growth,  the  needs  of  the  plant  for  water  probably 
increase  about  as  the  rate  of  growth  increases.  From  ear- 
liest spring  the  water-need  of  a  plant  increases,  until  it 
reaches  a  maximum  about  the  time  of  flowering,  after 
which  it  gradually  diminishes.  This  supposition,  as  will 
later  be  shown,  is  confirmed  by  actual  field  experiments. 

95.  Conditions  of  growth. — Many  factors  influence, 
to  some  degree,  the  rate  of  growth  of  a  crop.  Most  of 
them  are  uncontrollable  and,  therefore,  of  little  impor- 
tance to  the  farmer.  Those  that  concern  him  most, 
especially  under  arid  conditions  are  (1)  heat,  (2)  light,  (3) 
oxygen,  (4)  mineral  food  and  (5)  moisture  supply.  With 
given  vitality  and  inherent  qualities,  these  factors  will 
act  vigorously  upon  the  assimilation  of  carbon.  If  the 
temperature  is  too  low,  the  life  activities  of  the  plant 
become  slower  and  may  finally  cease.  The  higher  the 
temperature,  within  a  rather  large  range,  the  more  rapidly 
does  growth  go  on.  Light,  especially  sunlight,  is  another 
powerful  factor  in  furthering  the  assimilation  of  carbon. 
Oxygen  is  a  prime  factor  in  plant-growth,  for  without  it 
the  processes  of  oxidation,  corresponding  to  breathing  in 
the  higher  animals,  cannot  proceed;  and,  without  this 
function,  plant  life  cannot  long  persist.  There  must  be, 
therefore,  an  abundance  of  fresh  air  playing  about  the 


THE  WATER-COST  OF  DRY  MATTER  131 

plant.  Mineral  food,  though  taken  up  in  small  quanti- 
ties, is  indispensable  to  plant-growth.  Through  the  action 
of  the  mineral  foods,  the  most  complicated  processes  of 
the  plant  are  initiated  and  completed.  Finally,  carbon 
assimilation  and  growth  cannot  proceed  unless  there  is 
a  sufficient  supply  of  moisture  in  the  soil.  The  heat  and 
light  factors  cannot  well  be  controlled  by  the  farmer; 
the  mineral  food  can  be  controlled  in  part,  but  under  con- 
ditions of  irrigation  the  moisture  environment  of  plant 
roots  may  be  rather  easily  controlled.  It  is  of  first  impor- 
tance, therefore,  to  the  irrigation  farmer,  to  know  in  what 
way  variation  in  the  moisture  supply  will  affect  the  total 
production  of  dry  matter  of  the  crop  he  is  growing. 

96.  The  transpiration  ratio. — Dry  matter  is'  that 
part  of  a  plant  which  remains  when  all  the  water  has 
been  driven  off  by  heat  near  the  temperature  of  boiling 
water.  It  is  the  only  part  of  a  plant  of  real  value  to  the 
farmer  in  disposing  of  his  crops  for  purposes  of  food, 
clothing  or  shelter,  for  the  water  contained  in  vegetable 
substances  is  of  little  more  value  than  water  drawn  from  a 
stream.  The  quantity  of  dry  matter  produced  is,  more- 
over, the  best  agricultural  measure  of  the  sum  of  the  activi- 
ties of  a  crop  during  the  growing  season. 

The  water-cost  of  the  dry  matter  of  plants  may  be 
expressed  in  various  ways.  The  simplest  and  most  easily 
understood,  for  the  purposes  of  this  chapter,  is  to  speak 
of  the  number  of  pounds  of  water  used  in  the  production 
of  one  pound  of  dry  matter.  This  method  of  expressing 
the  water-cost  of  dry  matter  has  been  adopted  by  most 
investigators  of  the  subject,  and  it  is,  therefore,  well 
established. 

The  pounds  of  water  required  for  one  pound  of  dry 
matter,  may,  however,  be  determined  in  two  ways.  Water 


132 


IRRIGATION  PRACTICE 


is  taken  up  by  the  roots,  passed  through  the  plant  and 
evaporated  at  the  leaves  throughout  the  season.  The 
pounds  of  water  thus  actually  passing  through  the  plant 
for  each  pound  of  dry  matter  produced,  give  the  trans- 
piration ratio.  Under  agricultural  conditions,  however, 
as  water  passes  through  the  plant,  some  water  is  also 
evaporated  from  the  soil  surrounding  the  plant.  This 

direct  loss  from 
the  soil  surface, 
if  completely 
checked,  would 
seriously  hinder 
plant-growth.  The 
pounds  of  water 
passing  through 
the  plant  and 
evaporating  from 
the  soil  belonging 
to  the  plant,  for 
each  pound  of  dry 

matter     produced, 


FIG.  23.  Stomatal  apparatus  in  carnation  leaf 
through  which  transpiration  occurs. 


giye 


transpiration  ratio.  Students  of  this  subject  have  not 
always  carefully  distinguished  between  these  ratios;  con- 
sequently, in  modern  agricultural  books,  the  two  ratios 
are  found  in  the  same  tables  as  meaning  the  same  thing. 
Of  the  two  ratios,  the  evapo-transpiration  ratio  is  more 
nearly  the  measure  of  the  true  agricultural  needs  of  the 
plant. 

In  the  earlier  investigations  of  the  water-cost  of  dry 
matter  it  was  dimly  thought  that,  possibly,  under  all 
conditions,  an  invariable  relationship  existed  between 
the  quantities  of  water  transpired  and  of  dry  matter  pro- 


THE  WATER-COST  OF  DRY  MATTER 


133 


duced — that  the  transpiration  ratio  would  always  be  the 
same.  If  the  increase  in  dry  matter  were  thus  always  pro- 
portional to  the  quantity  of  water  transpired,  it  would 
simplify  greatly  many  important  problems  of  agriculture. 
Such  a  definite  relationship,  however,  was  not  found,  and 
it  is  now  well  known  that  every  agricultural  practice 
influences  not  only  the  assimilation  of  carbon  but,  also, 
transpiration,  though  not  always  to  the  same  degree  or 
in  the  same  direction.  Transpiration  and  the  production 
of  dry  matter  are  only  in  part  interdependent;  to  a  much 
larger  degree  they  are  independent  of  each  other.  This 
is  a  fundamental  thesis  of  irrigation  agriculture. 

Many  investigators  have  determined  the  number  of 
pounds  of  water  required  for  the  production  of  one  pound 
of  dry  matter  of  various  crops  on  a  variety  of  soils  and  in 
several  countries  of  the  world.  Some  of  these  determina- 
tions are  collected  in  the  following  table: 


Transpiration  ratio 

Evapo-transpiration 
ratio 

§ 

x. 

•a°8*> 

>»"o5 

5 

J3 

4 

V 

£>> 

111 

II 

1 
1 

§2 

.13 
f 

n 

§1 
P 

p 

Wheat 

247 

338 

546 

850 

1  017 

Barley     .... 

257 

680 

464 

774 

Oats    

376 

870 

504 

665 

Corn    

386 

450 

270 

552 

233 

Clover     

269 

310 

577 

Peas 

259 

273 

843 

830 

477 

1,118 

416 

It  may  be  noted  that  the  transpiration  ratios  are  lower 
in  England  and  Germany,  under  humid  conditions,  than 
in  Utah  and  India,  under  arid  conditions.  This  is  a  general 


134 


IRRIGATION  PRACTICE 


rule.  Further,  the  transpiration  ratios  vary  considerably, 
even  under  similar  conditions  of  humidity  or  aridity, 
varying  from  247  to  870  pounds  of  water  for  one  pound 
of  dry  matter.  As  would  be  expected,  the  evapo-transpira- 
tion  ratios  are  higher  than  the  transpiration  ratios.  The 
variation  among  the  evapo-transpiration  ratios  is  also 
large,  varying  from  270  to  1,118  pounds  of  water  for  one 
pound  of  dry  matter. 

The  data  in  the  above  table  may  well  be  used  to  show 
the  average  limits  of  the  magnitudes  of  the  transpiration 
and  evapo-transpiration  ratios  on  good  soils  of  the  stand- 
ard crops  in  different  parts  of  the  world;  for,  of  the  thou- 
sands of  determinations,  not  included  in  the  table,  nearly 
all  fall  within  the  limits  here  given.  Yet,  in  a  given  locality, 
the  transpiration  ratio  is  not  even  approximately  constant, 
unless  the  many  factors  concerned  in  plant-growth  and  in 
evaporation  are  constant.  The  variability  of  the  water- 
cost  of  dry  matter  is  well  brought  out  in  the  following 
table,  which  shows  the  range  of  transpiration  ratios  for 
certain  standard  crops  in  India  and  in  Utah: 

TRANSPIRATION  RATIO 


Crop 

India. 
Leather 

Utah.  Widtsoe 

Wheat  

422-1  133 

258-2  017 

Oats 

490-1  117 

Barley 

422-    679 

.... 

Corn      .    . 

246-    804 

151-1  012 

Peas  

453-    973 

269-1  658 

For  wheat,  the  range  was  in  India  from  422  to  1,133 
pounds  of  water,  and  in  Utah  from  258  to  2,017  pounds  of 
water  for  each  pound  of  dry  matter  produced.  Other 


THE  WATER-COST  OF  DRY  MATTER 


135 


crops  varied  in  very  much  the  same  manner.  Whether 
countries  or  various  fields  of  the  same  crop  in  the  same 
country  are  compared,  the  water-cost  of  dry  matter  will 
vary  widely. 

Meanwhile,  under  conditions  of  normal  fertility  and 
a  favorable  growing  season,  the  transpiration  ratios  fall 


FIG.  24.  Determining  the  transpiration  ratio. 


within  rather  definite  limits.  In  fact,  under  normal  con- 
ditions, the  evapo-transpiration  ratio  varies  from  250  to 
1,000  pounds  of  water  for  each  pound  of  dry  matter.  This 
gives  a  basis  for  an  estimate  of  the  quantity  of  water 
required  for  the  production  of  a  good  crop  of  wheat  or 
other  standard  crops.  For  example,  a  crop  of  wheat 


136  IRRIGATION  PRACTICE 

yielding  thirty  bushels  of  grain  to  the  acre,  if  250  pounds 
of  water  are  required  for  one  pound  of  dry  matter,  would 
require  throughout  the  season  5  acre-inches  of  water;  if 
500  is  the  transpiration  ratio,  10  inches  would  be  required, 
and  if  1,000  is  the  transpiration  ratio  20  inches  would  be 
required.  A  fair  crop  of  wheat  requires  annually,  con- 
sidering the  quantity  that  evaporates  directly  from  the 
surface,  from  5  to  20  inches  throughout  the  season.  This 
then  gives  a  fairly  safe  basis  on  which  to  establish  a 
duty  of  water. 

97.  The  seasons. — The  seasons,  including  sunshine, 
temperature,  relative  humidity  and  all  other  climatic 
factors,  are  of  first  importance  in  determining  the  acre- 
yield  of  crops.  In  fact,  for  the  production  of  dry  matter, 
the  seasons  overshadow  any  other  one  natural  factor,  and 
usually  is  as  important  as  the  cultural  operations.  In 
irrigated  sections,  where  water  is  added  at  will,  the 
influence  of  the  season  is  usually  underestimated,  for  on  a 
good  and  well-tilled  soil,  even  though  the  season  is  unfa- 
vorable, the  application  of  a  sufficient  quantity  of  water 
makes  the  crop  sure.  Nevertheless,  in  the  irrigated  sec- 
tions, as  elsewhere,  the  seasons  determine  the  average 
crop-yields  for  the  season,  whether  they  shall  go  high  or 
fall  low. 

The  seasons  also  determine  in  large  measure  the  quan- 
tity of  water  used  in  the  production  of  one  pound  of  dry 
matter.  At  the  Utah  Station,  in  a  series  of  experiments 
covering  several  years,  it  was  found  that,  under  con- 
ditions otherwise  nearly  identical,  the  transpiration 
ratio  for  wheat  varied  from  season  to  season,  the  range 
being  from  280  to  577.  In  1902,  the  transpiration  ratio 
for  wheat  was  402;  in  1903,  284;  in  1904,  577;  in  1905,  280, 
and  in  1908,  357.  Leather,  working  under  East  Indian 


THE  WATER-COST  OF  DRY  MATTER  137 

conditions,  obtained  similar  results.  The  transpiration 
ratio  of  wheat  varied  from  season  to  season  from  507 
to  883,  and  of  corn  from  332  to  477.  Both  the  Utah  and 
the  Indian  experiments  showed,  for  all  crops  investiga- 
ted, a  similar  seasonal  variation  in  the  water-cost  of  dry 
matter.  Whenever  the  season  is  favorable  for  the  produc- 
tion of  much  dry  matter,  the  water-cost  is  reduced;  that 
is,  a  good  season  produces  not  only  a  large  yield,  but  pro- 
duces it  with  a  relatively  small  quantity  of  water.  A 
poor,  backward  season  not  only  produces  a  small  quantity 
of  dry  matter,  but  produces  it  at  a  high  water-cost.  The 
variation  in  the  water-cost  of  dry  matter,  with  the  sea- 
sons, is  much  less  than  that  of  the  total  yield,  as  determined 
by  the  seasons.  The  water-cost  is,  however,  influenced 
materially  by  the  general  seasonal  conditions. 

98.  The  soil. — The  vital  relation  of  the  soil  to  crops 
would  naturally  suggest  that  the  quantity  of  water 
required  to  produce  one  pound  of  dry  matter  would  be 
partly  determined  by  the  nature  of  the  soil.  This  has  been 
conclusively  demonstrated  by  many  elaborate  investiga- 
tions. Pagnoul,  working  in  France,  found  that  the  trans- 
piration ratio  of  fescue  grass  on  a  fertile  soil  was  555;  on 
an  infertile  soil,  1,190.  In  the  Utah  experiments,  the 
transpiration  ratio  for  corn  was  386  on  College  loam,  408 
on  Sanpete  clay,  561  on  sand,  and  601  on  clay.  Similar 
variations,  some  much  larger,  were  observed  with  other 
crops  on  similar  soils.  For  corn,  the  transpiration  ratio 
varied,  according  to  the  soil  used,  from  432  to  579;  for 
wheat,  from  466  to  849.  Similar  results  could  be  quoted 
in  great  abundance  to  substantiate  the  statement  that 
the  nature  of  the  soil  is  a  determining  factor  in  the 
relative  quantity  of  water  used  by  the  plant  for  the 
production  of  a  given  quantity  of  dry  matter. 


138  IRRIGATION  PRACTICE 

The  physical  and  the  chemical  properties,  as  well  as 
the  depth  of  the  soil,  are  of  importance  in  determining  the 
water-cost  of  dry  matter.  The  deeper  the  soil  is,  the 
smaller  is  the  transpiration  ratio.  This  is  to  be  expected, 
for  the  deeper  the  soil  the  more  complete  will  the  root- 
development  be;  and  the  more  extensive  the  root-system 
is,  the  more  easily  may  water  and  the  mineral  foods  be 
obtained.  Thus,  carbon  assimilation  and  all  the  other 
vital  functions  of  the  plant  are  stimulated  into  action. 
Leather  grew  crops  in  jars  of  different  sizes,  and,  almost 
invariably,  found  that  the  crops  grown  in  large  jars 
were  produced  at  the  smallest  water-cost.  While  the 
depth  of  the  soil  is  an  incidental  factor,  it  may  at  times 
be  of  considerable  importance.  There  is,  throughout  the 
irrigated  region,  a  tendency  to  use  very  large  quantities 
of  seed.  Unless  the  soil  is  deep  and  easily  penetrated,  the 
mass  of  roots,  resulting  from  the  large  quantity  of  seed, 
may  not  find  sufficient  space  in  which  to  develop  prop- 
erly. The  resulting  crowding  and  overcrowding  lead  to 
immense  numbers  of  stunted  individual  plants,  that  do 
not  always  possess  the  vigor  to  use  water  to  the  best 
advantage.  This  is  of  particular  importance  wherever 
hardpan  is  near  the  surface,  or  where  a  heavy  clay  under- 
lies the  top  soil.  Moderate  quantities  of  seed  should  be 
sown,  even  under  irrigation. 

The  relation  of  the  physical  composition  of  a  soil  to 
the  water-cost  of  the  plant  grown  has  not  been  thoroughly 
investigated.  It  was  observed,  however,  long  ago,  that 
in  the  use  of  water,  a  loam  soil  is  more  economical  than 
a  sand  soil.  It  seems  that,  with  given  conditions  of 
fertility,  the  finer  the  soil  the  smaller  is  the  transpira- 
tion ratio.  Soils  rich  in  clay  or  fine  sand  are  naturally 
more  economical  of  water  than  are  those  containing  coarse 


THE  WATER-COST  OF  DRY  MATTER  139 

sand  or  poor  in  clay.  However,  the  fertility  of  the  soil, 
as  expressed  in  plant-food  content,  or  in  good  structure, 
seems  to  be  of  more  importance  than  the  texture  of  the 
soil.  Any  fertile  soil,  of  whatever  texture,  will  produce 
dry  matter  at  about  the  same  cost  of  water,  providing  all 
other  factors  are  approximately  the  same. 

99.  Mineral  food  or  soil  fertility.— The  fertility  of  a 
soil,  especially  as  measured  in  mineral  food,  is  a  large 
determining  factor  in  the  water-cost  of  dry  matter.  It 
has  been  shown  in  Chapter  VI  that  transpiration  is 
affected  by  the  dissolved  mineral  constituents  of  the  soil. 
The  actual  quantity  of  water  required  to  produce  one 
pound  of  dry  matter  is,  likewise,  materially  influenced  by 
the  mineral  plant-food  in  the  soil.  In  practically  every 
investigation,  from  the  first  to  the  latest,  soils  rated  as 
fertile,  because  of  their  large  annual  yields,  invariably 
yielded  dry  matter  at  a  lower  water-cost  than  less  fertile 
soils.  This  law,  that  crops  grown  on  fertile  soils  are  pro- 
duced at  a  lower  cost  than  those  grown  on  an  infertile 
soil,  has  been  especially  brought  out  by  the  diminished 
water-cost  of  crops  grown  on  soils  to  which  commercial 
fertilizers  have  been  applied.  The  Utah  experiments 
showed  that,  on  moderately  fertile  soils,  the  transpiration 
ratio  could  be  varied  from  247  to  639  by  applying  very 
small  quantities  of  commercial  fertilizers.  On  two  very 
infertile  soils,  the  transpiration  ratio  due  to  fertilizers  was 
reduced,  in  the  case  of  the  sand  from  1,012  to  459,  and  in 
the  case  of  the  clay  from  1,331  to  445.  Soils  of  high  fer- 
tility, however,  did  not  respond  to  the  application  of 
fertilizers  so  far  as  the  water-cost  of  dry  matter  was 
concerned.  Leather,  working  under  Indian  conditions, 
came  to  the  conclusion  that  suitable  manures  enable  plants 
to  economize  water  in  the  production  of  dry  matter  As 


140  IRRIGATION  PRACTICE 

an  average  of  many  experiments,  crops  were  produced  on 
unmanured  soils  with  a  transpiration  ratio  of  782;  and  on 
manured  soils  with  a  transpiration  ratio  of  572.  Bouyoucos 
has  concluded,  from  a  series  of  carefully  conducted  tests, 
that  the  greater  the  concentration  of  the  soil  solution, 
that  is,  the  more  substances  it  holds  in  solution,  the 
smaller  the  transpiration  ratio.  Fertile  soils  are  usually 
more  soluble  than  infertile  ones,  and  the  soil  solution  of 
fertile  soils  is  usually  more  concentrated.  The  same 
investigator  has  also  shown  that  as  the  soil  solution 
becomes  richer  in  soil  constituents,  the  cell  sap  of  the 
plant  becomes  more  concentrated,  and  that  this  may  be 
the  reason  that  less  water  enters  the  plant  daily  when 
the  concentration  of  the  soil  solution  is  high. 

Different  substances  influence  the  transpiration  ratio 
differently.  Acids,  for  instance,  tend  to  accelerate  trans- 
piration, and  to  increase  the  transpiration  ratio.  Alkalies 
have  the  opposite  effect.  This  is  of  importance  to  the 
irrigated  sections,  since  under  arid  conditions  alkaline, 
rather  than  acid,  soils  are  naturally  produced.  Lime, 
phosphoric  acid,  potash  and  nitrates  tend,  especially, 
to  reduce  the  water-cost  of  dry  matter.  Of  first  impor- 
tance are  the  nitrates.  The  richer  the  soil  is  in  nitrates, 
the  more  surely  will  the  water-cost  of  the  crop  be  reduced. 
This  law  appears  and  reappears  in  investigations  on  all 
manner  of  soils,  from  all  parts  of  the  world.  The  main- 
tenance of  an  abundance  of  nitrates  in  the  soil  is  undoubt- 
edly of  prime  importance  in  reducing  the  water  needs  of 
crops.  Increasing  the  concentration  of  the  soil  solution 
reduces  the  transpiration  ratio  only  when  the  substances 
held  in  solution  in  the  soil  moisture  are  true  plant-foods. 
Bouyoucos  showed  that  a  solution  of  common  salt,  or 
sodium  sulfate,  or  other  substances,  not  direct  plant- 


THE  WATER-COST  OF  DRY  MATTER  141 

foods,  reduced  the  rate  of  transpiration,  but  did  not 
diminish  the  water-cost  of  the  resulting  dry  matter.  It 
does  not  follow,  therefore,  that  on  alkali  soils,  such  as 
occur  frequently  in  the  arid  West,  crops  may  be  produced 
at  a  lower  water-cost  than  on  soils  containing  less  soluble 
matter.  Whether  or  not  water  is  saved  depends  entirely 
upon  the  composition  of  the  alkali.  In  places,  the  alkali 
consists  largely  of  nitrates,  potassium  salts  and  other  plant- 
foods;  but,  ordinarily,  alkali  lands  contain  the  chlorides, 
sulfates  and  carbonates  of  sodium  and  other  substances 
of  a  non-nutrient  character.  Crops  grown  on  the  usual 
alkali  lands  are  not  only  injured  by  the  high  concentra- 
tion of  the  soil  solution,  but  they  are  produced  at  an  exces- 
sive cost  of  water. 

The  irrigation  farmer  who  wishes  to  make  the  best 
use  of  a  limited  quantity  of  water  must  keep  steadily  in 
mind  the  necessity  of  maintaining  the  soil,  constantly, 
in  a  very  fertile  condition. 

100.  Cultural  operations. — It  is  well  understood  that 
thorough  plowing,  frequent  cultivation  and  other  correct 
cultural  operations  accelerate  soil  solubility  and  favor 
bacterial  activity  in  the  soil.  Nitrification,  the  conversion 
of  the  soil  nitrogen  into  nitrates,  is  especially  fostered  by 
proper  soil  tillage.  This  treatment  given  soils  should, 
therefore,  affect  quite  distinctly  the  water-cost  of  crops. 
Few  experiments  have  been  made  on  this  subject,  but 
those  available  bear  out  this  belief.  At  the  Utah  Sta- 
tion, a  number  of  pots  containing  soils  of  varying  degrees 
of  fertility  were  sown  to  corn.  Half  of  the  pots  were 
properly  cultivated,  and  the  others  received  no  culti- 
vation, throughout  the  growing  season.  The  transpira- 
tion ratio  was  invariably  smaller  on  the  cultivated  than 
on  the  non-cultivated  soils.  On  College  loam,  the  ratios 


142  IRRIGATION  PRACTICE 

on  the  cultivated  and  on  the  non-cultivated  pots  were 
252  and  603;  on  a  sandy  clay,  428  and  535,  and  on  an 
infertile  clay,  582  and  750.  It  so  happened  that  the  Col- 
lege loam  was  a  self-mulching  soil,  on  which  ordinary 
cultivation  did  not  lessen  direct  evaporation.  The  favor- 
able effect  of  cultivation  was  shown,  however,  in  the  great 
reduction  in  the  water-cost  of  dry  matter  resulting  from 
simple  tillage.  On  every  hand  the  proper  cultivation 
of  the  soil  is  shown  to  be  a  means  of  economizing  water. 
It  prevents  the  direct  evaporation  of  water  from  the  soil; 
it  reduces  the  transpiration,  and  it  makes  it  possible  to 
produce  dry  matter  at  a  low  water-cost.  There  is  much 
truth  in  the  statement  of  the  irrigation  farmer  that  culti- 
vation may  take  the  place  of  water.  Within  certain  limits, 
it  may  be  said  that  tillage  is  water.  Water  is  indispensa- 
ble for  the  production  of  crops,  but  the  need  for  water 
may  be  tremendously  reduced  if  the  upper  layer  of  soil 
is  thoroughly  cultivated. 

All  other  correct  treatments  of  the  soil  have  pretty 
much  the  same  effect.  At  the  Utah  Station,  a  series  of 
soils  were  cropped  every  year  for  three  years,  while  another 
similar  series,  receiving  identical  treatment,  were  left 
bare  for  three  years.  The  fourth  year,  all  the  soils  were 
planted  to  corn.  The  soils  that  had  lain  fallow  for  three 
years  invariably  produced  dry  matter  at  a  lower  water- 
cost  than  did  those  which  has  been  cropped.  The  trans- 
piration ratios  for  the  fallow  and  the  cropped  soils  were, 
on  the  College  loam,  573  and  659;  on  Sanpete  clay  550 
and  889,  on  clay  1,739  and  7,466.  Irrigated  soils  are 
cropped  every  year,  and  fallowing  is  scarcely  ever  prac- 
tised under  irrigation.  In  fact,  none  of  the  established 
systems  of  irrigation-farming  include  the  fallow  year. 
Under  dry-farm  conditions,  on  the  other  hand,  fallow- 


THE  WATER-COST  OF  DRY  MATTER  143 

ing  is  almost  indispensable.  Fallowing  may  be  replaced 
by  crops  such  as  corn  or  sugar  beets,  which  receive  culti- 
vation throughout  the  season  and  thereby  set  free  plant- 
food  for  the  following  crop.  It  is  probable,  however,  that, 
even  under  conditions  of  irrigation,  as  in  the  West, 
where  land  is  plentiful  and  water  scarce,  it  may  in  the 
end  be  profitable  to  observe  the  occasional  clean  fallow  of 
the  land.  The  resting  period  not  only  helps  to  destroy 
weeds,  plentiful  under  irrigation,  but  enables  the  soil  to 
resume  a  natural  physical  condition,  to  set  free  plant- 
food  and  to  start  again  a  favorable  bacterial  flora.  The 
value  of  fallowing  is  well  shown  is  another  of  the  Utah 
experiments.  One  series  of  soils  had  been  cropped  steadily 
for  four  years;  another  series  had  been  cropped  only  4hree 
out  of  four  years,  and  still  another  series  had  been  cropped 
only  one  year  out  of  four.  These  three  series  of  soils  were 
left  exposed  to  the  elements  for  three  years;  that  is,  they 
received  a  three-years'  fallow.  They  were  then  all  sown 
to  corn,  which  grew  and  flourished  well.  The  transpira- 
tion ratios,  determined  for  each  series  of  soils,  were  almost 
identical.  This  shows  that  the  three  years  of  fallow  had 
restored  the  three  soils  to  an  approximate  equality  of 
fertility,  so  far  as  water-consumption  was  concerned, 
although  at  the  beginning  of  the  period,  they  had  been 
left  widely  different  by  the  various  treatments  they 
had  received.  The  fallow  period,  objectionable  chiefly 
because  of  the  chance  it  gives  the  organic  matter  to  be 
oxidized  by  the  air,  has  great  advantages  in  restoring  the 
soil  to  a  condition  where  crops  may  be  produced  at  a  low 
water-cost. 

101.  The  vigor  of  the  plant. — Whenever  the  seasons, 
the  nature  of  the  soil,  the  available  plant-food,  the  treat- 
ment of  the. soil;  the  factors  above  discussed,  favor  vigor- 


144  IRRIGATION  PRACTICE 

ous  plant-growth,  they  also  tend  to  diminish  the  quantity 
of  water  required  for  the  production  of  one  pound  of  dry 
matter.  That  is,  so  far  as  these  factors  are  concerned,  as 
the  plant  becomes  more  and  more  thrifty  the  smaller 
becomes  the  transpiration  ratio.  The  more  vigorous  a 
plant  is,  the  more  economically  can  it  use  the  water  at 
its  disposal. 

102.  Varying  quantities  of  water. — Of  greatest  impor- 
tance in  the  consideration  of  the  economical  use  of  water 
by  plants  is  the  effect  of  varying  quantities  of  water. 
Under  irrigation,  much  or  little  water  may  be  applied 
at  the  will  of  the  farmer.  Upon  the  proper  manipulation 
of  this  characteristic  factor,  irrigation  agriculture  will 
stand  or  fall.  It  is,  therefore,  of  prime  importance  to 
know  how  the  production  of  crops  is  affected  when  the 
quantity  of  water  applied  is  varied. 

Many  experiments  on  this  subject  have  been  made 
Jately,  but  not  enough  to  set  forth  fully  the  principles 
involved.  Most  of  the  leading  students  of  water  in  rela- 
tion to  agriculture  have  lived  in  humid  countries,  where 
the  only  important  control  of  soil  water  is  the  conserva- 
tion of  the  rain — or  snow-water — in  the  soil  upon  which 
it  falls.  Only  in  recent  years  has  serious  attention  been 
given  to  the  subject  from  the  direct  point  of  view  of  irriga- 
tion. Moreover,  most  of  the  experiments  on  this  subject, 
many  of  high  value,  have  been  made  in  pots,  under  con- 
ditions not  strictly  comparable  with  the  conditions  of 
practical  irrigation.  Usually,  the  soils  have  been  main- 
tained at  definite  degrees  of  wetness.  To  maintain  these 
conditions,  water  was  added  to  the  pots  every  day  or 
every  few  days,  so  that  it  could  be  said,  at  the  end  of  the 
experiment,  that  the  soil  had  been  kept  practically  at 
that  degree  of  saturation  throughout  the  whole  experi- 


THE  WATER-COST  OF  DRY  MATTER  145 

mental  period.  Under  irrigation,  the  method  is  quite 
different,  for  the  water  is  applied  at  relatively  long  inter- 
vals, and  when  the  available  soil  moisture  has  been  largely 
removed  by  the  growing  crop.  The  saturation  of  the  soil 
falls,  therefore,  from  high  to  low,  between  successive 
irrigations. 

All  experiments  on  the  subject,  whether  in  pots  or  in 
the  field,  show  that,  as  a  general  rule,  the  more  water 
offered  the  plant,  within  practical  limits,  during  the  grow- 
ing season,  the  larger  the  total  yield  of  dry  matter.  The 
increase  in  dry  matter  due  to  the  increase  in  soil-saturation 
falls  upon  every  part  of  the  plant — roots,  stems  and  leaves. 
Von  Seelhorst  and  Tucker,  among  the  early  experimenters 
in  this  domain,  showed,  in  a  series  of  carefully  conducted 
tests,  that  the  whole  oat  plant — heads,  straw  and  roots — 
increased  as  the  water  in  the  soil  increased.  In  the  pots  con- 
taining a  low  percentage  of  water,  591  grams  of  the  whole 
plant  were  obtained;  in  the  pot  with  a  medium  percentage 
of  water,  725  grams,  and  in  the  pots  with  a  high  percent- 
age of  water,  922  grams.  In  most  experiments,  only  the 
parts  of  the  plants  harvested  by  the  farmer  are  considered, 
so  that  this  experiment,  is  of  special  importance.  The 
increase  in  the  total  yield  of  dry  matter  does  not,  however, 
continue  indefinitely,  as  the  soil-saturation  increases. 
Mayer,  who  was  one  of  the  first  to  study  the  effect  of 
varying  quantities  of  water,  found  that  for  rye,  wheat, 
barley  and  oats,  the  yield  increased  with  the  increase  in 
soil-saturation  up  to  a  certain  point,  after  which  there 
was  a  strong  diminution  in  the  yield  of  dry  matter.  Experi- 
ments made  elsewhere  bear  out  this  conclusion.  As  a 
further  general  rule,  then,  increasing  the  soil  moisture 
increases  the  production  of  dry  matter  only  within  cer- 
tain definite  limits.  If  too  much  water  is  applied  to  the 
j 


146  IRRIGATION  PRACTICE 

soil  during  the  season,  there  is  a  diminution  instead  of 
an  increase  in  the  yield  obtained. 

This  question,  however,  remains:  As  the  dry  matter 
increases  with  the  increase  in  soil  saturation,  does  the 
water-cost  of  each  pound  of  dry  matter  remain  the  same? 
This  matter  has  been  investigated  with  considerable 
care  and  with  concordant  results.  Wilms  found  that 
with  a  little  water  the  transpiration  ratio  for  potatoes 
was  39;  with  more  water,  50;  and  with  much  water,  61. 
The  Utah  experiments  showed  invariably  that  with  wheat, 
sugar  beets,  corn,  potatoes,  alfalfa  and  all  other  crops 
tested,  as  the  quantity  of  water  used  was  increased  and 
the  yield  thereby  increased,  the  water-cost  also  became 
larger.  The  general  law  is  that,  within  the  limits  of 
practical  irrigation,  the  transpiration  ratio  increases  as 
the  quantity  of  water  added  to  the  soil  increases;  that  is, 
that  the  water-cost  of  crops  becomes  larger  as  more  water 
is  used  in  irrigation.  Lyon  and  a  number  of  his  co-workers, 
notably  Morgan  and  Harris,  as  well  as  other  students, 
have  confirmed  this  law,  until  it  may  be  accepted  as 
being  securely  established.  This  is  a  matter  of  tremend- 
ous importance.  By  using  more  water,  the  irrigation 
farmer  obtains  a  larger  yield,  but  less  for  each  unit  of 
water  used.  The  question  will  always  be,  With  how  much 
water  will  he  get  the  largest  possible  returns  from  the 
use  of  his  land,  water  and  labor? 

The  only  field  experiments  of  any  magnitude  con- 
ducted with  a  view  of  testing  the  effect  of  various  quan- 
tities of  water  on  the  production  of  dry  matter  and  on 
the  water-cost  of  dry  matter  are  those  of  the  Utah  Sta- 
tion. Other  experiments,  not  reduced  to  dry  matter,  will 
be  noted  in  later  chapters.  In  the  following  table  the 
yields  of  dry  matter  in  pounds  to  the  acre;  with  varying 


THE  WATER-COST  OF  DRY  MATTER 


147 


quantities  of  water  and  on  a  deep  fertile  soil,  are  shown 
for  four  of  the  standard  crops.  The  results  are  averages 
of  a  large  number  of  experiments,  and  may  be  accepted 
as  being  tolerably  accurate  for  the  climate  of  the  inter- 
mountain  region. 

YIELDS  OP  DRY  MATTER  IN  POUNDS  PER  ACRE  WITH  VARYING 
QUANTITIES  OF  WATER 


Inches  of 
water  applied 

Wheat 

Corn 

Sugar  beets            Potatoes 

5.0 

4,969 

...                 6,080 

2,310 

7.5 

5,545 

10,757 

. 

2,730 

10.0 

5,684 

12,762 

8,053 

2,925 

15.0 

6,279 

13,092 

8,636 

3,405 

20.0 

13,856 

10,076 

4,095 

25.0 

6,672 

14,606 

30.0 

.    .    .                15,294 

10,271 

3,660 

35.0 

7,229                  .    .    . 

. 

50.0                   7,999                  .    .    . 

11,528 

*3,795 

55.0                   .    .    . 

12,637 

.    .    . 

*45  inches. 

An  examination  of  the  above  table  will  show  that  as 
the  quantity  of  irrigation  water  was  increased  throughout 
the  season,  the  yield  of  wheat  increased  without  inter- 
ruption; the  corn  increased  up  to  30  inches,  but  fell  at 
55  inches;  the  sugar  beets  and  the  potatoes  increased 
without  interruption.  This  is  in  accordance  with  the  law 
above  stated  that,  as  water  is  increased  the  general  ten- 
dency of  the  yield  of  crops  is  to  increase.  The  soil  was  deep 
and  porous,  into  which  even  very  large  quantities  of  water 
sank  to  great  depths.  Thus,  the  soil  was  never  over- 
saturated,  but  with  large  irrigations  the  soil-water  film 
continued  longer  to  be  of  maximum  thickness  than  with 
small  irrigations.  Even  under  these  favorable  conditions, 
the  yield  of  corn  diminished  after  30  inches  of  water  had 


148 


IRRIGATION  PRACTICE 


been  applied,  and  the  yields  of  other  crops,  not  given  in 
the  table,  likewise  diminished  after  certain  limits  l\ad  been 
reached.  Undoubtedly,  had  more  water  been  used  than 
the  maximum  in  the  above  table,  or  if  the  soil  had  been 
shallower  or  less  fertile,  there  would  have  been  a  strong 
falling  off  in  the  yields  of  all  the  crops. 

In  the  following  table  the  evapo-transpiration  ratios 
of  the  above  yields  under  varying  applications  are  given: 

POUNDS  OF  WATER  REQUIRED  TO  PRODUCE  ONE  POUND  OF  DRY 
M.4.TTER  WITH  VARYING  QUANTITIES  OF  WATER 

(Evapo-transpiration  ratio) 


Inches 
of  water 
applied 

Wheat 

Corn 

Alfalfa 

Sugar  beets 

Potatoes 

5.0 

856 

569 

1,136 

7.5 

869 

276 

1,136 

10.0 

948 

275 

62l 

57  i 

1,255 

15.0 

1,038 

356 

977 

663 

1,411 

20.0 

416 

946 

682 

1,466 

25.0 

1,317 

474 

1,052 

. 

30.0 

.    . 

527 

1,253 

889 

2,242 

35.0 

1,530 

. 

. 

45.0 

. 

. 

3,060 

50.0 

1,809 

. 

1,480 

1,186 

55.0 

1,087 

•    • 

3,292 

Without  exception,  when  small  quantities  of  water 
are  applied,  the  water-cost  is  low;  as  larger  quantities  are 
applied,  the  water-cost  becomes  greater  and  greater.  By 
increasing  the  total  quantity  of  water  throughout  the 
season,  the  evapo-transpiration  ratio  or  the  pounds  of 
water  for  one  pound  of  dry  matter  increased  for  wheat 
from  850  to  1,809;  for  corn,  from  255  to  1,087;  for  alfalfa, 
from  641  to  1,480;  for  sugar  beets,  from  569  to  1,186,  and 
for  potatoes,  from  1,136  to  3,292.  While,  therefore,  there 
is  a  distinct  increase  in  dry  matter  as  more  water  is 


>/SflOO 


f 


Depth  of  irrigation  Water  Applied  (inches) 

FIG.  25.  Yield  of  dry  matter  of  cereals  with  varying  quantities  of  water. 


try  Matter  per  Acre  tof* 
^irrigation  Water 

\  1  1 

\ 

\ 

V 

\ 

\ 

5 

\ 

\ 

\\ 

a 

» 

\ 

E 

- 

\ 

\ 

X, 

^ 

\ 

v 

^^ 

^^ 

Pounds  of  A 
One  inch  o/ 

I  i 

8 

i!S 

^ 

x 

"  — 

"  1 

•—  .^ 

- 

,  ?*, 

X; 

"^ 

Ci. 
>— 

== 

S£S, 

S«>=E 

•~^, 

-0 

^^-* 

-  — 

±± 

5~^ 

"*•** 

^^, 

—  . 

-- 

S            JO            /S           SO           IS            30           3S           40          4S           SO         £f 

Depth  of  irrigation  Water  Applied  f  inches  ) 

G.  26.  Yield  of  dry  matter  of  cereals  per  inch  of  irrigation  water. 

(149) 


150 


IRRIGATION  PRACTICE 


applied,  this  increase  is  obtained  at  a  distinctly  higher 
water-cost.  Moderate  irrigations  are  always  most  eco- 
nomical. 

The  same  figures  are  presented  in  a  more  practical 
manner  in  the  following  table,  in  which  are  shown  the 
yields  in  pounds  of  dry  matter  to  the  acre  for  each  inch 
of  irrigation  water  under  varying  total  irrigations: 

POUNDS  OF  DRY  MATTER  PER  ACRE  PER  INCH  OF  IRRIGATION  WATER 


Inches 
of  water 
applied 

Wheat 

Corn 

Alfalfa 

Sugar  beets 

Potatoes 

5.0 

994 

1,216 

462 

7.5 

739 

1,434 

. 

364 

10.0 

568 

1,276 

909 

805 

293 

15.0 

419 

873 

463 

576 

227 

20.0 

693 

418 

504 

200 

25.0 

267 

584 

344 

. 

. 

30.0 

. 

510 

342 

122 

35.0 

207 

. 

271 

. 

m 

45.0 

. 

t 

< 

84 

50.0 

160 

199 

231 

. 

55.0 

•    • 

230 

•    • 

•    • 

•    • 

It  is  clear  from  the  data  of  this  table  that,  so  far  as 
water  is  concerned,  it  is  more  profitable  to  use  small  than 
large  quantities  of  water.  As  the  total  seasonal  quantity 
of  water  increased,  the  acre-yield  of  dry  matter,  for  each 
inch  of  irrigation  water,  varied  for  wheat  from  994  to 
160  pounds;  for  corn,  from  1,434  to  230  pounds;  for 
alfalfa,  from  909  to  199  pounds;  for  sugar  beets,  from  1,216 
to  231  pounds,  and  for  potatoes  from  462  to  84  pounds. 
These  are  tremendous  reductions  with  increasing  appli- 
cations of  water,  which  of  necessity  must  be  considered 
in  the  establishment  of  a  consistent  practice  of  irrigation, 
having  as  its  purpose  the  reclamation  of  the  largest  pos- 


THE  WATER-COST  OF  DRY  MATTER 


151 


sible  area  in  the  arid  regions.  However  true  it  may  be,  in 
the  humid  regions,  that  the  acre-yield  is  the  all-important 
thing,  in  arid  regions  the  yield  to  the  acre-inch  or  to  the 
unit  of  water  is  equally  important.  For  each  crop  and 
given  conditions,  a  point  must  be  determined  at  which 
the  highest  possible  returns  may  be  obtained  from  the 
land,  water  and  labor  employed.  (Figs.  25,  26.) 

103.  Maximum  yield  with  given  quantity  of  water. — 
The  relation  of  varying  quantities  of  water  to  the  yields 
of  crops  may  be  expressed  also  by  showing  the  producing 
power  of  a  definite  quantity  of  water,  say  30  acre-inches, 
when  spread  over  1,  2,  4  or  6  acres.  This  is  done  in  the 
following  table: 

POUNDS  OF  DRY  MATTER  PRODUCED  BY  30  ACRE-INCHES  OF  WATER 


Crop 

Spread  over 

Ratio 

1  acre 

4  acres 

Wheat         .            .... 

6,951 
15,294 
8,133 
10,271 
3,660 

22,180 
43,028 
32,072 
28,268 
10,920 

3.19 
2.81 
3.94 
2.75 
2.98 

Corn    

Alfalfa     

Sugar  beets    

Potatoes  

When  30  acre-inches  were  made  to  cover  4  acres 
instead  of  1  acre,  the  yield  was  increased  for  wheat  nearly 
three-fold,  for  alfalfa  nearly  four-fold,  for  sugar  beets 
nearly  three-fold  and  for  potatoes  nearly  three-fold.  When 
it  is  considered  that  the  development  of  the  arid  regions 
will  depend  upon  the  settlement  of  a  dense  population, 
requiring  food,  clothing  and  shelter,  it  is  evident  that 
irrigation  water,  the  limiting  factor  of  the  prosperity  of 
the  region,  must  be  made  to  produce  the  largest  quan- 
tities of  materials  for  food,  clothing  and  shelter.  The 
acre-yield,  the  criterion  of  humid  regions,  will  retreat 


FIG.  27.  Crop-producing  power  of  30  acre-inches  (wheat) 


\ 
I 


32OOO 


\teooo 


8OOO 


"50-tfcnt 

yc/K 

vert 

ffcne 


.  28.  Crop-producing  power  of  30 
acre-inches  (alfalfa). 


(152) 


THE  WATER-COST  OF  DRY  MATTER 


153 


before  the  acre-inch  yield,  the  criterion  of  irrigated  regions. 
The  understanding  of  this  principle  must  be  brought 
into  the  practices  of  the  people,  and  must  reshape  the 
irrigation  laws  of  the  states  and  federal  government,  if 
the  greatest  prosperity  shall  be  won  for  the  West.  In 
the  day  to  come,  it  is  probable  that  no  farmer,  though  he 
own  an  abundance  of  water,  will  be  allowed  to  use  more 


§32000 


24000 


8000 


Stigar&eels 


Fio.  29.  Crop-producing  power  of  30  acre-inches  (sugar  beets) 

than  the  quantity  determined  upon  by  the  state  as  being 
the  best. 

The  evils  of  over-irrigation  are  many.  In  addition  to 
those  mentioned,  it  is  shown  in  this  chapter  that  the  large 
acre-use  of  water  may  diminish  the  actual  yield  an  acre, 
and  invariably  does  make  the  crop  more  expensive  from 
the  point  of  view  of  the  water  used  for  each  unit  of  dry 
matter.  The  permanence  of  irrigation-farming  depends 
on  the  moderate  use  of  water.  (Figs.  27-29.) 


154 


IRRIGATION  PRACTICE 


104.  The  nature  of  the  crop. — The  nature  of  the  plant 
is  a  factor  in  the  economical  production  of  dry  matter. 
Little  is  as  yet  known  as  to  the  special  properties  of  the 
plant  that  affect  the  water-cost  of  dry  matter;  but,  it  is 
certain  that  plants  differ  in  their  water  requirements.  A 
number  of  interesting  results  have,  indeed,  been  obtained, 
as  for  example,  Montgomery's  observation  that  narrow- 
leaved  corn  uses  less  water  to  produce  a  pound  of  dry 
matter  than  does  corn  with  wider  leaves.  Attempts  have 
often  been  made  to  classify  crops  in  accordance  with 
their  water  needs,  but  seldom  under  irrigated  conditions. 

Some  crops  always  yield  largely,  others  lightly.  This 
differing  power  is  inherent  in  the  crops,  and  is  generally 
beyond  the  farmers'  control,  for  the  variations  in  yield 
due  to  cultural  methods  are  within  rather  narrow  limits. 
The  results  of  the  Utah  work  has  made  possible  the 
arrangements  of  the  crops  in  the  order  of  their  acre- 
yield  of  dry  matter,  as  in  the  following  table: 


Order  of  acre-yield  of  dry 
matter,  beginning  with  the 
highest 

Pounds  of  water  for  one  pound  of  dry 
matter  (evapo-transpiration  ratio) 

10  inches 

25  inches 

1.  Corn        

275 
569 
571 
604 
621 
872 
869 
1,255 
(2,170) 
(2,214) 

474 
760 
786 
998 
1,052 
871 
1,317 
1,854 
(2,557) 
(4,248) 

2.  Carrots  

3.  Sugar  beets    

4.  Barley    

5  Alfalfa 

6.  Oats 

7.  Wheat 

8.  Potatoes     

9.  Onions    

10.  Cabbage     

With  light,  medium  and  heavy  irrigations,  the  order 
was  practically  the  same.  Corn  yielded  the  largest  quan- 
tity of  dry  matter  to  the  acre ;  Italian  rye  grass,  the  smallest. 


THE  WATER-COST  OF  DRY  MATTER  155 

To  the  irrigation  farmer,  a  large  yield,  however,  is  of 
interest  only  if  it  is  produced  with  little  water.  In  the 
second  and  third  columns  of  the  preceding  table,  therefore, 
are  shown  the  pounds  of  water  required  for  one  pound  of 
dry  matter,  or  the  evapo-transpiration  ratio,  when  10 
and  when  25  inches  were  used.  The  uniform  variation 
is  remarkable.  There  was  a  steady  diminution  in  the 
evapo-transpiration  ratio,  from  corn  to  the  lowest  yielder. 
In  the  case  of  the  two  exceptions,  oats  and  wheat,  and 
corn  and  carrots,  the  yields  were  almost  identical.  Only 
under  the  25-inch  heading  was  there  a  notable  exception — 
that  of  oats.  The  variation,  however,  is  so  regular,  over 
so  large  a  range  of  crops,  that  it  may  be  suggested,  as  a 
law,  that  the  water-cost  of  dry  matter  varies  inversely 
as  the  inherent  power  of  the  plant  to  produce  dry  matter 
per  acre.  That  is,  the  crop  that  yields  most  largely  pro- 
duces the  yield  at  the  lowest  water-cost.  It  may  be 
observed  in  this  connection  that  the  crops  that  yield  most 
heavily  with  the  least  expenditure  of  water  are  those  of 
the  longest  growing  period. 

Summary. — The  factors  that  determine  the  water- 
cost  of  dry  matter  fall  into  two  classes:  First,  those 
like  the  season,  nature  of  the  soil,  mineral  food,  tillage, 
vigor  of  plant  and  nature  of  plant,  that  favor  the  produc- 
tion of  dry  matter,  and  at  the  same  time  diminish  the 
rate  of  transpiration  and  reduce  the  water-cost  of  dry 
matter;  and,  second,  those,  like  the  varying  quantity  of 
water,  that  favor  the  production  of  dry  matter,  but  at 
the  same  time  accelerate  transpiration  and  increase  the 
water-cost  of  dry  matter.  All  these  factors  are  of  great 
importance  in  the  establishment  of  practices  for  the 
economical  production  of  dry  matter,  but,  the  last,  the 
varying  quantity  of  water,  because  it  is  under  the  easy 


156  IRRIGATION  PRACTICE 

control  of  the  irrigation  farmer,  and,  because  its  effects 
are  large,  is  of  greatest  importance. 

REFERENCES 

BOUYOUCOS,  G.  J.  Transpiration  of  Wheat  Seedlings  as  Affected 
by  Soils,  by  Solutions  of  Different  Densities,  and  by  Various 
Chemical  Compounds.  Proceedings  of  the  American  Society 
of  Agronomy,  Vol.  Ill,  p.  130  (1911). 

BRIGGS,  LYMAN  J.,  and  SHANTZ,  H.  L.  The  Water  Requirements  of 
Plants.  United  States  Department  of  Agriculture,  Bureau  of 
Plant  Industry,  BuUetins  Nos.  284  and  285  (1913). 

FORTIER,  SAMUEL.  Soil  Moisture  in  Relation  to  Crop- Yield.  Mon- 
tana Experiment  Station,  Ninth  Annual  Report  (1902). 

HARRIS,  F.  S.  Effects  of  Varying  Soil-Moisture  Content  on  Certain 
Properties  of  the  Soil  and  on  the  Growth  of  Wheat.  Cornell 
University,  Doctor's  Thesis  (1911). 

HARRIS,  F.  S.  Long  versus  Short  Periods  of  Transpiration  in 
Plants  Used  as  Indicators  of  Soil  Fertility.  Proceedings  of  the 
American  Society  of  Agronomy,  Vol.  Ill  (1910). 

KHANKHAJE,  P.  S.  Some  Factors  Which  Influence  the  Water  Require- 
ments of  Plants.  Journal  American  Society  of  Agronomy,  Vol. 
VI,  p.  1  (1914). 

KING,  F.  H.    The  Physics  of  Agriculture.    Second  edition  (1901). 

LEATHER,  J.  W.  Water  Requirements  of  Crops  in  India.  Agricul- 
tural Institute,  Pusa,  Memoirs  of  the  Department  of  Agricul- 
ture in  India,  Part  I,  Vol.  I,  No.  8,  (1910);  Part  II,  Vol.  I,  No. 
10  (1911). 

MAYER,  A.  Ueber  den  Einfluss  Kleineren  oder  Grosseren  Mengen 
von  Wasser  auf  die  Entwickelung  einiger  Kulturpflanzen. 
Journal  fur  Landwirtschaft,  Band  46,  S.  167  (1898). 

MONTGOMERY,  E.  G.  Correlation  Studies  of  Corn.  Nebraska 
Experiment  Station,  Twenty-fourth  Annual  Report,  p.  109, 
especially  p.  150  (1911). 

MONTGOMERY,  E.  G.,  and  KIESSELBACH,  J.  A.  The  Relation  of 
Climatic  Factors  to  the  Water  Used  by  the  Corn  Plant. 
Nebraska  Experiment  Station,  Twenty-fourth  Annual  Report, 
p.  91  (1911). 


THE  WATER-COST  OF  DRY  MATTER  157 

MORGAN,  J.  O.  The  Effect  of  Soil  Moisture  and  Temperature  on 
the  Availability  of  Plant  Nutrients  in  the  Soil.  Proceedings 
of  the  American  Society  of  Agronomy,  Vol.  Ill,  p.  191  (1911). 

SEELHORST,  C.  VON,  and  TUCKER,  G.  M.  Der  Einfluss,  welcher  der 
Wassergehalt  u.  s.  w.  auf  die  Ausbilding  der  Haferpflanze, 
Journal  fur  Landwirtschaft,  Band  46,  52  (1898). 

WIDTSOE,  J.  A.  The  Chemical  Life  History  of  Lucern.  Part  I. 
Utah  Experiment  Station,  Bulletin  No.  48  (1896). 

WIDTSOE,  J.  A.  Factors  Influencing  Transpiration  and  Evaporation. 
Utah  Experiment  Station,  Bulletin  No.  105  (1905). 

WIDTSOE,  J.  A.   Dry-Farming.   Chapter  IX  (1911). 

WIDTSOE,  J.  A.  The  Production  of  Dry  Matter  with  Different 
Quantities  of  Irrigation  Water.  Utah  Experiment  Station, 
Bulletin  No.  116  (1912). 

WILLARD,  R.  E.,  and  HUMBERT,  E.  P.  Soil  Moisture.  New  Mexico 
Experiment  Station,  Bulletin  No,  86  (1913). 


CHAPTER  VIII 
CROP  DEVELOPMENT  UNDER  IRRIGATION 

THE  total  yield  of  a  crop  is,  usually,  of  first  impor- 
tance; but,  frequently,  a  particular  part  of  the  plant 
commands  a  much  higher  value  than  some  other  part. 
Thus,  the  seed  of  wheat,  oats,  barley,  rye,  corn  and  the 
other  grains,  has  a  much  higher  value  than  the  straw; 
and  the  tops  of  sugar  beets  have  comparatively  little 
value,  while  the  roots  bring  high  money  returns.  For  such 
plants,  it  is  as  important  to  regulate  the  proportion  of 
plant  parts  as  to  produce  a  large  yield  of  the  whole  plant. 
The  whole  crop  of  alfalfa  and  the  hay  crops  generally,  is 
sold,  but  the  nutritive  value  of  the  hay,  per  pound, 
depends  on  the  relative  proportion  of  the  stalks  and 
leaves,  since  the  leaves  are  much  more  nutritious  than  are 
the  stalks.  The  farmer  prefers  leafy  plants,  and  it  is 
important  to  know  under  what  conditions  of  irrigation 
the  largest  proportion  of  leaves  may  be  obtained. 

In  yet  another  way  is  this  matter  important.  The 
grains,  the  grasses  and  many  other  crops  are  harvested 
only  for  the  parts  above  ground.  The  roots  are  left  in 
the  ground  to  decay  and  have  no  direct  money  value. 
The  substances  elaborated  in  the  plant  are  rather  easily 
moved  from  place  to  place,  and,  under  certain  cultural 
treatments,  it  is  conceivable  that  much  of  the  nutritive 
material  of  the  plant  may  move  into  the  roots  and  remain 
there  when  the  plant  is  harvested.  The  farmer  needs  to 
know,  therefore,  under  what  conditions  of  irrigation  the 

(158) 


CROP  DEVELOPMENT  UNDER  IRRIGATION        159 

largest  possible  proportion  of  the  material  formed  in  the 
plants  may  be  retained  in  above-ground  parts  which  are 
harvested.  In  the  case  of  root  crops,  the  reverse  is  desired. 
The  roots  possess  the  highest  value,  the  tops  the  smallest 
and  therefore  the  largest  possible  proportion  of  the  plant 
constituents  should  be  found  in  the  roots  at  the  time 
of  harvest. 

Moreover,  it  is  of  interest  and  often  of  importance  to 
know  in  what  way  the  general  growth  of  the  plant  is 
affected  by  varying  methods  of  irrigation.  To  understand 
thoroughly  the  principles  underlying  the  art  of  .irriga- 
tion, it  is  not  sufficient  to  know  how  much  crop  by  weight 
is  produced  by  given  quantities  of  water  applied  in  given 
ways,  but  it  is  equally  important  to  know  in  what  way 
the  various  parts  of  the  plant  are  affected  in  their  growth 
by  such  variations  in  irrigation. 

105.  Response  to  irrigation. — The  plant  responds 
quickly  to  irrigation.  In  irrigation,  water  is  applied  at 
infrequent  intervals.  At  first  the  soil  is  very  wet;  then  it 
gradually  dries,  until  it  reaches  the  lento-capillary  point 
or  even  the  wilting  point;  then  it  is  again  wet,  again  dry, 
and  so  on  throughout  the  season. 

All  the  life  processes  of  plants  growing  on  irrigated 
land  become  very  active  as  soon  as  water  is  applied  to 
the  soil.  Under  conditions  of  irrigation,  therefore,  the 
plant  is  somewhat  intermittent  in  its  growth.  Assimila- 
tion and  all  other  processes  favoring  growth  are  espe- 
cially rapid  after  each  irrigation,  gradually  diminishing  in 
intensity  and  almost  ceasing  before  the  next  irrigation. 

In  the  Utah  experiments,  for  instance,  it  was  found 
that  during  the  first  week  after  irrigation  of  peas,  more 
than  500  pounds  of  dry  matter  were  added  to  the  weight, 
and  of  oats,  more  than  700  pounds  of  dry  matter  were 


160 


IRRIGATION  PRACTICE 


added  to  the  acre.  Such  large  gains,  could  not,  of  course, 
continue  for  any  length  of  time  without  resulting  in  total 
yields  far  above  the  maximum  for  the  crops  in  question. 

Many  of  the  effects  of  irrigation  are  more  clearly 
understood  if  it  is  kept  in  mind  that  the  crop  responds 
readily  to  the  application  of  water. 


FlG.  30.  Effect  of  little,  medium  and  much  water  on  wheat. 

106.  Proportion  of  roots. — The  vigor  and  general 
condition  of  the  plant  depend  largely  upon  the  develop- 
ment of  the  root-system.  In  the  early  stages  of  growth, 
the  plant  uses  most  of  the  materials  gathered  from  the 
air  and  soil  for  the  development  of  large  and  numerous 
roots,  which,  radiating  through  the  soil,  may  readily 
absorb  water  and  plant-food.  When  the  roots  are  well 
developed,  carbon-assimilation  by  the  leaves  is  hastened, 
and  growth  is  rapid.  Later  in  the  life  of  the  plant,  root- 
growth  becomes  slower  and  slower,  and  the  energies  of  the 
plant  are  more  largely  directed  to  the  development  of 
the  parts  above  ground.  When  at  last  the  stems  are  well 


CROP  DEVELOPMENT  UNDER  IRRIGATION      161 

developed  and  a  sufficient  quantity  of  materials  has  been 
stored  in  the  various  plant  organs,  growth  diminishes, 
flowers  and,  later,  seeds  are  developed.  This  is  the 
natural  course  of  plant-growth.  It  is  indispensable  that 
in  the  beginning  the  plant  be  given  every  possible  chance 
to  develop  its  root-system. 

It  has  long  been  known  that  a  dry  soil  is  more  com- 
pletely filled  with  roots  than  is  a  wet  one.  Under  dry- 
farm  conditions,  for  instance,  wheat  roots  penetrate 
heavy  clay  soils  to  a  depth  of  8  feet  or  more.  No  special 
attention  was  at  first  given  to  this  observation,  because, 
under  the  humid  conditions  prevailing  in  the  earlier  inves- 
tigations of  agriculture,  there  seemed  to  be  no  practical 
method  of  regulating  the  quantity  of  water  in  the  soil 
during  the  growing  season.  The  rain  came  as  it  willed, 
irrespective  of  the  needs  of  the  farmer.  During  the 
last  few  years,  however,  this  matter  has  been  given 
quantitative  investigation.  Von  Seelhorst  and  Tucker 
found  that,  of  the  whole  oat  plant,  including  the  under- 
and  above-ground  parts,  when  little  water  was  used, 
about  13  per  cent  was  contained  in  the  roots;  when 
much  water  was  used,  about  7.5  per  cent  was  found 
in  the  roots.  With  barley,  wheat,  peas,  and  other  simi- 
lar crops,  it  has  likewise  been  shown  that  the  total  and 
relative  weights  of  roots  are  largest  when  little  water 
is  used.  In  the  Utah  work,  it  was  found  that  the  propor- 
tion of  sugar  beets  or  potatoes  to  the  parts  above  ground 
was  not  greatly  affected  by  the  quantity  of  water  used. 
In  fact,  the  tendency  seems  to  be  that  specialized  roots 
and  tubers  increase  slightly  in  proportion  to  the  whole 
plant  as  the  quantity  of  water  is  increased.  It  may, 
however,  be  stated,  as  a  law  fairly  well  established,  that 
the  roots  of  plants,  at  least  of  annual  plants,  always  form 

K 


162  IRRIGATION  PRACTICE 

a  larger  proportion  of  the  whole  plant  when  the  soil  is 
kept  somewhat  dry  throughout  the  growing  season.  The 
roots  seem  to  go  in  search  of  water  and  food,  when  little 
is  at  hand,  thus  increasing  the  root-development.  It  does 
not  follow  that  the  actual  weight  of  roots  produced  in 
dry  soil  is  much  larger  than  when  produced  in  wet  soil. 
The  experiments  conducted  on  the  subject  indicate 
that  the  total  weight  is  somewhat  larger  in  dry  than  in 
wet  soil;  but,  the  differences  are  not  great  and  do  not 
approximate  the  differences  in  the  proportions  of  roots 
in.  the  whole  plant. 

Gain  has  conducted  a  number  of  especially  valuable 
experiments  on  this  subject  and  has  come  to  the  conclus- 
ion that,  whenever  little  water  is  added,  the  main  or 
primary  roots  are  large  and  well  developed,  while  the  side 
or  secondary  roots  are  small  and  poorly  developed.  If 
much  water  is  used,  the  main  roots  are  smaller  and  the 
side  roots  become  relatively  larger.  That  is,  with  little 
water  a  much  larger  volume  of  soil  is  reached  by  the  root- 
system  than  when  much  water  is  used. 

The  lesson  to  the  irrigation  farmer  is  clear.  A  plant 
with  a  small  root-system,  poorly  developed,  cannot  make 
as  good  use  of  the  water  added  to  the  soil,  or  of  the  food 
in  the  soil,  as  can  a  vigorous  plant.  It  is  important, 
therefore,  that  as  early  as  possible  the  root-system  be 
made  large  and  well  developed.  When  this  has  been 
accomplished,  water  may  be  added  in  considerable  quan- 
tities without  the  fear  that  plant  roots  are  unable  to  make 
proper  use  of  it.  As  intimated  above,  to  develop  a  large 
root-system  it  is  necessary  to  keep  the  soil  only  mode- 
rately wet  in  early  spring.  In  districts  where  the  winter 
precipitation  is  fairly  large,  deep  irrigated  soils  are  fairly 
well  stored  with  moisture  in  the  spring,  at  the  time  of 


CROP  DEVELOPMENT  UNDER  IRRIGATION      163 

seeding.  If  irrigation  is  applied  very  early  to  such  lands, 
the  root-system  is  likely  to  be  retarded  in  its  growth,  and 
the  final  crop-yield  may  be  greatly  reduced.  On  soils 
practically  saturated,  at  planting  time,  from  the  winter 
rains  and  snows,  the  first  irrigation  should  be  postponed 
as  long  as  possible  so  that  a  strong  root-system  can  be 
developed  to  use  fully  the  water  applied  plentifully  later 
in  the  season.  This  doctrine  has  been  confirmed  by  many 
experiments  under  true  irrigated  conditions.  For  instance, 
in  districts  where  the  winter  precipitation  is  so  high  (say 
8  inches  during  the  six  months  of  fall  and  winter)  that 
the  soil  to  a  depth  of  10  to  12  feet  is  approximately 
saturated,  no  benefits  result  from  irrigation  immediately 
after  sowing;  and  the  effect  of  the  first  irrigation  becomes 
greater  as  it  is  removed  in  time  from  the  date  of  seeding. 

Naturally,  however,  where  the  climatic  conditions  are 
such  that  at  seeding  time  the  soil  is  not  well  filled  with 
water,  thorough  irrigation  immediately  before  or  after 
planting  would  do  much  to  insure  a  proper  germination 
of  the  seeds  and  a  more  rapid  development  of  the  root- 
system.  Even  when  this  is  done,  the  longer  the  first 
irrigation  is  postponed,  the  better  it  will  be  for  the  crop, 
which  then  can  better  develop  its  root-system.  Let  it 
not  be  forgotten  by  the  irrigation  farmer  that,  in  a  rela- 
tively dry  soil,  roots  will  develop  faster  and  will  go  more 
vigorously  in  search  of  water  and  food. 

107.  Proportion  of  leaves  and  stems.— The  part  of 
the  plant  above  ground  is  also  definitely  affected  by 
the  quantity  of  water  applied.  As  the  water  applied  to  the 
soil  increases,  the  whole  plant  becomes  longer.  This  is 
true  with  all  the  common  crops,  such  as  wheat,  oats, 
barley,  rye,  beans  and  buckwheat.  Every  farmer  has 
observed  that  in  fields  to  which  water  is  added  abundantly 


164  IRRIGATION  PRACTICE 

the  grain  and  hay  stand  high,  and  often  the  grain  crops 
become  so  tall  that  they  fall  over  and  give  a  great  deal  of 
trouble  at  harvest  time.  Similarly,  it  is  commonly 
observed  that  with  little  water  the  crops  are  short.  Under 
dry-farming  conditions,  where  the  rainfall  is  small,  the 
wheat  is  usually  so  short  that  instead  of  binders,  which 
cannot  be  used,  headers  are  employed  which  simply  cut 
off  the  heads  of  the  grain  leaving  the  high  straw  standing. 
Further,  as  irrigation  water  is  increased,  the  clusters  of 
seed-bearing  heads  increase  in  number.  The  general 
appearance  of  the  plant,  therefore,  depends  on  the  quan- 
tity of  water  added  to  the  soil  during  the  growing  season. 

Of  chief  importance  is  the  effect  of  varying  quanti- 
ties of  water  upon  the  stooling  of  the  grains,  that  is,  the 
number  of  seed-producing  stalks  from  one  seed.  The 
more  water  is  used,  the  more  profuse  becomes  the  stooling; 
the  less  water  is  used,  the  less  stooling  occurs.  This  is  of 
particular  importance  wherever  the  seed  is  the  chief 
product  at  the  harvesting. 

In  practically  every  experiment  conducted  on  this 
subject,  however,  it  has  been  found  that,  while  the  length 
of  the  plant  and  the  number  of  seed-bearing  stalks  increase 
as  the  water  increases,  there  is  a  limit  to  this  correlation. 
The  increase  due  to  the  increased  irrigation  continues  only 
up  to  a  definite  limit,  beyond  which,  if  more  water  is 
added,  a  diminution  occurs  and  the  plant  becomes  shorter, 
the  seed-bearing  stalks  less  developed  and  with  fewer 
seeds,  and  growth  is  arrested.  A  medium  quantity  of 
water  would  therefore  be  better  than  a  very  large  quan- 
tity to  produce  large  plants  with  many  seeds. 

The  nature  of  the  leaves  is  influenced  by  the  applica- 
tion of  water.  With  little  water  the  leaves  of  the  grains 
are  distinctly  green  and  firm;  with  much  water,  they  are 


CROP  DEVELOPMENT  UNDER  IRRIGATION      165 

pale  green  and  soft.  In  the  case  of  corn,  it  has  been  shown, 
also,  that  with  little  water  the  leaves  are  narrow  and 
pointed,  whereas  with  much  water  they  are  wide  and 
more  rounded,  and  their  screw-like  turning  increases. 
Wilms  showed  that,  in  the  case  of  potatoes,  a  small  amount 
of  water  produced  a  thick  leaf  containing  long  cells  and 
few  stomata  or  breathing  pores  per  square  inch,  while 
much  water  produced  thinner  leaves  containing  short 
cells  and  many  more  stomata  per  unit  of  surface.  That 
is,  in  color,  form,  consistency,  cell-structure,  and  other 
properties,  both  the  leaves  and  the  stems  respond  definitely 
to  varying  quantities  of  water.  This  emphasizes  the  power 
of  the  irrigation  farmer,  by  merely  varying  the  quantity 
of  water  applied  to  plants,  ta  change  the  color  of  the  plant, 
the  stiffness  of  the  stalks,  the  shape  of  the  leaves,  and 
many  other  similar  properties.  Every  part  of  the  plant  is 
changed  to  correspond  with  the  water  at  the  disposal  of 
the  plant. 

Of  more  direct  interest,  however,  to  the  farmer,  than 
the  size  and  shape,  is  the  relative  proportion  of  leaves, 
stalks  or  other  parts  of  a  crop.  The  leaves  of  plants, 
whether  large  or  small,  are  usually  of  higher  nutritive 
value  than  the  stalks.  It  is  desirable  therefore,  when  a 
crop  is  grown  for  forage  to  secure  the  largest  proportion 
of  leaves.  The  few  available  investigations  make  it  clear 
that  the  proportional  parts  of  leaves  and  stalks  are  dis- 
tinctly affected  by  the  quantity  of  water  used  in  irriga- 
tion. In  the  Utah  experiments,  with  wheat,  oats  and  peas, 
the  proportion  of  leaves  in  the  whole  plant  became  higher 
and  higher  as  the  water  was  increased,  whereas  with 
potatoes  the  reverse  occurred.  When  the  leaves  and 
stalks  alone  were  compared,  it  was  found  that,  as  with 
potatoes,  the  less  water  used  the  leafier  were  the  plants. 


166  IRRIGATION  PRACTICE 

In  general,  much  water  produces  at  first  leafy  plants; 
if  more  is  added,  the  proportion  is  diminished.  Crops 
grown  for  forage,  in  which  a  high  proportion  of  leaves  is 
desirable,  may  profitably  be  given  larger  quantities  of 
water  than  crops  that  are  grown  more  largely  for  some 
other  part  of  the  plant. 

108.  Proportion  of  heads  and  grain. — The  grain 
crops  are  grown  primarily  for  seed.  The  value  of  the 
straw  is  small  in  comparison  with  that  of  the  seed.  The 
grain  farmer  desires  therefore  to  convert  as  much  as  pos- 
sible of  the  plant  into  seed  at  the  time  of  harvest.  Up 
to  a  definite  limit,  the  clusters  of  seed-bearing  heads 
increase  with  the  quantity  of  water  used.  The  number 
of  seeds  in  each  head  of  wheat,  or  ear  of  corn  increases, 
likewise,  as  the  quantity  of  water  is  increased.  Even 
the  beard  in  the  bearded  varieties,  becomes  longer  or 
shorter  as  much  or  little  water  is  applied.  The  seed- 
bearing  part  of  plants,  like  the  roots,  stalks  and  leaves,  is 
sensitive  to  the  water  applied  to  the  soil. 

Many  reported  experiments  deal  with  the  proportions 
of  the  heads  in  grain  crops  as  influenced  by  varying 
quantities  of  water.  In  the  Utah  experiments  it  was 
found  that  as  the  total  quantity  of  irrigation  water  was 
increased  the  proportion  of  heads  in  the  plant  above 
ground  decreased  with  wheat,  from  38  to  25  per  cent; 
with  oats,  from  59  to  49  per  cent;  with  peas,  from  67  to 
48  per  cent.  In  every  case  it  was  distinctly  shown  that 
the  more  water  applied,  the  smaller  the  proportion  of 
the  heads  in  the  whole  plant.  Therefore,  while  the  size 
and  number  of  heads  seem  to  be  increased  as  the  total 
quantity  of  water  increases,  it  is  equally  clear  that  the 
stems  and  leaves  are  increased  more  markedly.  This 
leads  to  a  decreasing  proportion  of  heads  in  the  whole 


CROP  DEVELOPMENT  UNDER  IRRIGATION      167 

plant    as   the   water   applied   increases   throughout   the 
season. 

This  correlation  has  been  demonstrated  by  a  great 
number  of  investigators,  although  in  few  cases  only 
under  true  irrigated  conditions.  Hellriegel  was  one  of 
the  first  to  investigate  this  subject  and  to  announce  the 
law  that  the  proportion  of  seed  to  the  straw  in  all  ordi- 
nary crops  becomes  smaller  as  the  available  water  in  the 
soil  during  the  growing  season  increases.  Mayer,  working 
in  Holland,  investigated  rye,  wheat,  barley  and  oats, 
and  found  invariably  that  the  more  water  he  offered  the 
plants,  the  smaller  became  the  proportion  of  the  grain 
yielded  by  the  crops.  French  and  English  investigators 
have  confirmed  this  conclusion.  At  the  Utah  Station,  in 
a  long  series  of  experiments  under  irrigated  conditions,  the 
percentage  of  seed  in  the  harvests  of  wheat,  oats,  barley 
and  corn  was  very  carefully  determined.  In  the  following 
table  some  of  the  results  obtained  are  shown: 


Depth  of 

Percentage  of  grain  in  harvest  of 

(inches) 

Wheat 

Oats 

Barley 

Corn 

5.0-  7.5 

44.45 

64.54 

50.74 

51.69 

15.0 

40.83 

62.55 

47.09 

47.92 

25.0-35.0 

38.65 

38.27 

43.55 

45.0-50.0 

32.89 

57.63 

In  the  first  column  is  given  the  depth,  in  inches,  of 
the  water  applied  throughout  the  growing  season;  in  the 
following  columns,  for  each  crop,  the  percentage  of  grain 
in  the  total  harvest.  The  smallest  quantity  of  water 
applied  was  5  inches,  and  the  largest  50  inches.  The  small- 
est quantity  used  should  meet,  fairly,  ordinary  crop  needs, 
and  the  largest  quantity  used  is  not  very  far  above  that 


ira/t 


is  in. 

water 


25  in 
water 


50  /n 

water 


water 

FIG.  31.  Proportion  of  grain  and  atraw  with  varying  irrigations  (wheat). 


(168) 


CROP  DEVELOPMENT  UNDER  IRRIGATION      169 

actually  used,  though  wastefully,  in  many  of  the  irrigated 
sections. 

With  the  smallest  quantity  of  water,  nearly  45  per 
cent  of  the  total  wheat  crop  was  seed;  as  the  water  was 
increased,  the  percentage  became  smaller  and  smaller, 
until,  with  50  inches,  the  percentage  of  seed  in  the  crop 
was  less  than  33  per  cent.  In  a  similar  manner,  the  seed 
in  oats  fell  from  64  to  57  per  cent  as  the  water  was 
increased;  in  barley,  from  nearly  51  to  a  little  over  38 
per  cent,  and  in  corn,  from  nearly  52  to  about  43  per  cent. 

That  is,  under  irrigated  field  conditions,  the  law 
which  has  been  so  frequently  determined  in  pot  experi- 
ments has  been  fully  confirmed:  namely,  as  the  water 
available  to  plants  increases,  the  proportion  of  seed  in 
the  plants  decreases.  This  is  naturally  of  the  deepest 
significance  to  the  irrigation  farmer,  for  not  only  does 
the  total  yield  of  the  crop  per  unit  of  water  decrease 
largely  as -more  water  is  used,  but  the  proportion  of  the 
more  valuable  parts  of  the  plant  decreases  also.  The 
meaning  of  this  is  that,  if  the  yield  per  acre-inch  of 
water  of  the  whole  wheat  crop  is  diminished  as  more- 
water  is  used,  the  yield  of  grain  is  even  more  largely 
decreased.  The  grain  farmer  cannot,  therefore,  by  any 
process  of  reasoning  convince  himself  that  it  is  desirable 
to  use  very  large  quantities  of  water  for  the  production 
of  his  crops.  (Fig.  31.) 

It  may  be  said,  in  this  connection,  that  the  prevail- 
ing idea  that  grain  grown  with  little  water  is  not  so  full 
and  plump  as  that  produced  with  more  water,  is  erro- 
neous. This  phase  of  the  matter  will  be  discussed  in 
Chapter  XI. 

109.  Other  plant  parts. — The  development  of  crops 
under  the  influence  of  irrigation  as  here  outlined  is  fairly 


170  IRRIGATION  PRACTICE 

well  established  and  may  be  safely  accepted,  yet  it  is 
not  to  be  forgotten  that  much  work  must  yet  be  done 
with  the  various  crops  before  a  full  knowledge  of  the 
subject  is  in  our  possession.  We  may  say  with  a  certainty 
that  the  leaves,  stems,  seeds  and  roots  of  crops  are  influ- 
enced definitely  by  varying  the  quantity  of  irrigation 
water.  We  do  not  know  definitely,  however,  how  the 
yield  of  fruit  is  affected  by  varying  quantities  of  water, 
although  in  view  of  the  high  value  of  the  fruit  crop,  this 
is  a  particularly  important  need.  It  is  probably  true  that 
the  production  of  fruit  depends  upon  the  time  at  which 
water  is  applied  rather  than  upon  the  total  quantity  of 
water.  However,  from  early  springtime  each  tree  sends 
forth  its  leaves,  and  the  materials  elaborated  by  the 
leaves  are  distributed  throughout  the  whole  tree — to 
develop  roots,  trunk  and  branches,  and  to  produce  fruit. 
Undoubtedly,  the  quantity  of  water  applied  plays  an 
important  part  in  determining  how  these  elaborated 
materials  shall  be  used  in  the  tree.  In  so  large  a  struc- 
ture as  a  well-matured  fruit  tree  it  must  be  of  great  impor- 
tance to  know  how  the  materials  gathered  from  the  soil 
and  air  may  be  driven  into  the  fruit,  without  injuring  the 
well-being  of  trunk,  branches  and  roots  of  the  tree.  That 
the  fruit  crop  is  as  sensitive  as  other  crops  to  the  effects 
of  varying  quantities  of  water  is  well  shown  in  several 
experiments.  For  instance,  Jones  and  Colver,  in  a  study  of 
the  composition  of  irrigated  and  non-irrigated  fruits, 
conducted  under  the  auspices  of  the  Idaho  Experiment 
Station,  and  using  fruit  grown  under  the  somewhat 
humid  conditions  of  northern  Idaho,  found  that  the  pro- 
portion of  seeds,  skins  and  other  wastes  of  fruits  was 
high  or  low  as  the  fruit  was  or  was  not  irrigated.  The 
following  table  gives  some  of  the  results: 


CROP  DEVELOPMENT  UNDER  IRRIGATION      171 


Irrigated 

Non-irrigated 

Cherries   Bing                      

92.35 

87.30 

Plums   Green  Gage    

87.57 

77.36 

Prunes   Italian    

95.66 

93.00 

Apples   Arkansas  Black 

91  49 

90.02 

It  was  further  observed  that  the  various  parts  of  the 
waste  varied  with  the  water  used.  As  our  knowledge  of 
this  matter  grows,  it  will  no  doubt  be  possible,  under  con- 
ditions of  irrigation,  to  control  largely  the  output  of  fruit 
from  a  given  orchard. 

A  similar  problem  is  connected  with  the  production 
of  the  tomato,  which  is  grown  in  tremendously  large 
quantities  in  districts  where  the  canning  factories  operate. 
It  is  of  prime  importance  to  obtain  the  largest  yield  by 
weight  of  tomatoes,  considering  both  quality,  size  and 
shape.  To  make  the  vines  small  and  the  tomatoes  large  is 
a  question  of  very  great  importance.  The  same  may  be 
said  of  the  cantaloupe  industry,  which  assumes  large 
proportions  in  certain  sections  of  the  irrigated  West. 
The  agricultural  investigators  of  the  irrigated  regions 
must  take  these  matters  in  hand  at  an  early  date,  to  dis- 
cover the  laws  that  control  the  production  of  the  various 
parts  of  all  the  crops  that  are  commonly  grown  under 
irrigation. 

The  length  of  season  also  has  an  important  bearing 
upon  the  economy  of  the  water  used.  By  varying  the 
quantity  of  water  used,  it  is  possible,  at  least  in  a  small 
measure,  to  lengthen  out  or  shorten  the  season.  As  is 
well  known,  the  more  water  is  at  the  disposal  of  the  plant, 
the  longer  growth  continues.  If  the  soil  moisture  is  high 
in  early  spring,  there  is  a  tendency  for  the  plant  to  pre- 


172  IRRIGATION  PRACTICE 

pare  for  a  long  wet  season,  and  if  this  same  environment 
is  continued  throughout  the  season,  the  plant  continues 
the  vegetative  processes  much  longer  than  if  the  moisture 
from  the  earliest  period  is  relatively  low.  In  general, 
we  may  lay  down  the  law  that  the  more  water  used,  the 
longer  the  growing  season  of  the  plant;  the  smaller  the 
quantity  of  water  used,  the  shorter  its  growing  season. 
This  may  often  find  important  applications.  For  instance, 
wherever  early  and  late  frosts  prevail,  the  moderate 
use  of  water  will  hasten  maturity;  and,  in  hot,  dry  dis- 
tricts, the  moderate  use  of  water  will  prevent  an  unneces- 
sarily long  vegetative  period  with  rapid  evaporation. 

REFERENCES 

HARRIS,  F.  S.  The  Irrigation  and  Manuring  of  Corn.  Utah  Experi- 
ment Station,  Bulletin  No.  —  (1914). 

WIDTSOE,  J.  A.  The  Effect  of  Varying  Quantities  of  Irrigation 
Water  on  the  Production  of  Dry  Matter.  Utah  Experiment 
Station,  Bulletin  No.  116  (1912). 

WIDTSOE,  J.  A.,  and  STEWART,  ROBERT.  The  Effect  of  Irrigation 
on  the  Growth  and  Composition  of  Plants  and  Different  Periods 
of  Development.  Utah  Experiment  Station,  Bulletin  No.  116 
(1912). 


CHAPTER  IX 
THE  TIME  OF  IRRIGATION 

UNDER  ideal  conditions  of  irrigation,  a  plentiful  supply 
of  water  would  always  be  at  the  disposition  of  the  farmer. 
In  practice,  such  a  condition  seldom  exists.  The  flow  of 
water  in  the  rivers  from  which  the  canals  are  taken,  varies 
from  season  to  season,  and,  unless  the  water  is  stored  in 
reservoirs,  there  is  not,  throughout  the  season,  a  uniform- 
supply  of  water.  In  the  spring,  the  flow  is  beyond  the 
capacities  of  the  canals;  in  midsummer  and  later  it  is 
often  insufficient  for  the  needs  of  the  system.  Different 
crops  have  different  water  requirements,  both  as  to  total 
quantity  and  periodic  application.  Young  plants  use  less 
water  than  do  the  larger  and  stronger  plants  some  weeks 
older;  and  the  mature  plant,  the  life  activities  of  which 
have  ceased,  has  very  little  need  of  water.  The  life  his- 
tory of  the  plant  determines,  largely,  the  best  time  of 
irrigation.  It  seldom  happens,  however,  that  the  periodic 
natural  flow  of  water  coincides  with  the  periodic  crop 
requirements.  The  problem  of  applying  the  best  quantity 
of  water  at  the  proper  time,  which  will  determine  the 
principles  of  canal  management,  is  one  of  the  most  com- 
plex in  irrigation  practice. 

110.  The  ideal  principle. — It  may  be  laid  down  as 
an  ideal  principle,  that,  so  far  as  possible,  the  same 
percentage  of  moisture  should  be  maintained  in  the  soil 
throughout  the  growing  season,  irrespective  of  the  age 
of  the  plant.  That  is,  the  soil-water  film  should  be  kept 

(173) 


174  IRRIGATION  PRACTICE 

at  the  same  thickness  while  the  plant  is  growing.  The 
young  plant  requires  less  water  per  day  than  the  older 
plant,  but  the  ease  with  which  the  water  may  be  obtained 
should  be  practically  the  same  for  young  and  older  plants, 
as  long  as  they  are  growing  vigorously.  Such  a  condition 
of  uniform  water  content  in  the  soil  is  practically  impos- 
sible unless  water  is  added  daily  to  the  soil  to  replace  that 
lost  by  evaporation  and  transpiration.  The  intermit- 
tent nature  of  irrigation,  fundamentally  characteristic, 
implies  a  period  of  high  moisture  percentage  imme- 
diately after  an  irrigation,  gradually  diminishing  until, 
just  before  the  following  irrigation,  the  soil  is  often  very 
dry.  Nevertheless,  the  irrigation  farmer  must  attempt  to 
apply  irrigation  water  in  such  a  way  as  to  leave  the  plant 
in  an  approximately  uniform  moisture  environment 
throughout  the  season.  Therefore,  irrigation  must  be 
more  abundant  and  frequent  at  periods  of  high  transpira- 
tion. So  far  as  the  soil  is  concerned,  the  intermittent 
nature  of  irrigation  is  highly  favorable  in  producing  a 
condition  favorable  to  plant-growth. 

The  discussion  of  the  time  of  applying  irrigation  water 
may  be  surveyed  as  follows: 

1.  Irrigation  when  crop  is  not  growing. 

(a)  Fall  irrigation. 

(6)  Winter  irrigation. 

(c)  Early  spring  irrigation. 

2.  Irrigation  when  crop  is  growing. 

(a)  For  germination. 

(6)  Use  of  early  spring  floods. 

(c)  Irrigation  at  different  periods  of  crop  growth. 

(x)  Annuals. 

(y)  Biennials. 

(?)  Perennials. 


TIME  OF  IRRIGATION  175 

111.  Fall  irrigation. — Fall  irrigation  means  irrigation 
after  harvest,  but  before  winter  sets  in.  After  harvest, 
water  still  flows  down  the  river  channels  and  ordinarily 
goes  to  waste.  This  late  water  may  be  used  to  saturate 
the  soil,  and  thus  be  held  over  until  the  following  growing 
season.  In  districts  where  the  fall  and  winter  percipita- 
tion  is  insufficient  to  saturate  the  soil,  fall  irrigation  is 
especially  desirable. 

An  average  soil  of  the  arid  regions,  under  field  con- 
ditions, is  saturated  when  it-  contains  about  18  per  cent  of 
water  to  a  depth  of  10  feet.  This  is  equivalent,  approxi- 
mately, to  a  depth  of  3  feet  of  water.  Under  wise  systems 
of  cropping,  about  12  per  cent  of  water  is  left  in  the  soir 
to  a  depth  of  10  feet  at  the  time  of  harvest.  At  the  follow- 
ing seed  time,  the  soil  should  again  be  in  a  saturated  con- 
dition. The  difference  between  12  per  cent  and  18  per 
cent,  or  practically  1  foot  of  water,  should,  therefore,  be 
furnished  by  the  natural  precipitation,  or  by  fall,  winter 
or  spring  irrigation. 

Over  a  large  area  of  the  inter-mountain  country,  the 
precipitation  comes  chiefly  in  the  fall  and  winter  or  early 
spring,  that  is,  between  harvest  and  seed  time.  In  this 
district,  fall  and  winter  irrigation  have  little  value,  if  the 
land  is  so  treated  as  to  permit  the  storage  in  the  soil  of 
the  rain-  and  snow-water — unless  the  total  seasonal 
precipitation  is  low,  when  irrigation  during  the  fall  sea- 
son may  be  very  helpful.  In  other  sections,  much  of 
the  rainfall  comes  in  late  spring,  summer  or  early  fall, 
that  is,  during  the  growing  season.  This  water  does  not 
remain  stored  in  the  soil  during  the  winter  for  the  use 
of  next  season's  crop,  and  under  this  condition,  fall 
irrigation  is  highly  profitable. 

It  is  of  great  advantage  to  have  the  soil  saturated 


176  IRRIGATION  PRACTICE 

at  planting  time,  for  (1)  it  makes  possible  a  quicker  and 
more  complete  germination,  and  (2)  it  delays  the  time 
of  the  first  irrigation,  and  the  plant  is  enabled  to  estab- 
lish a  strong  root-system.  It  is,  also,  decidedly  advanta- 
geous to  keep  the  soil  well  saturated  with  water  through- 
out the  dormant  season.  Water  added  in.  the  fall  dis- 
tributes itself  in  the  usual  way  throughout  the  soil  to  a 
considerable  depth.  The  soil- water  film  then  remains 
long  in  intimate  contact  with  the  soil  particles;  plant- 
food  is  dissolved  and  well  distributed  throughout  the 
water  until,  at  planting  time,  the  soil-water  is  heavily 
charged  with  dissolved  plant-food  and  is  a  very  nutri- 
tious medium  for  plant-growth. 

Water  applied  during  the  growing  season  is  imme- 
diately drawn  upon  by  the  plant,  and  does  not  remain  in 
the  soil  long  enough  to  permit  of  extensive  solution  or 
distribution  of  soil  nutrients  in  the  soil-moisture  film. 
Only  the  portions  of  the  soil-water  film  that  lie  nearest 
to  the  soil  particles  become  rich  in  plant-food.  This  may 
be  the  one  explanation  of  the  repeated  observation  that 
a  given  quantity  of  water  applied  in  irrigations  at  inter- 
vals of  one,  two,  three  or  even  four  weeks  may  often 
yield  a  larger  crop  than  when  applied  in  smaller  and  more 
frequent  irrigations.  Water  applied  too  frequently  or  in 
small  quantities  is  pumped  out  of  the  soil  so  rapidly 
that  there  is  little  chance  for  solution  of  plant-food. 
With  longer  intervals  and  larger  irrigations,  more  plant- 
food  may  be  dissolved  and  used  in  plant-production. 

At  any  rate,  water  applied  in  the  fall  and  winter  sea- 
son has  the  opportunity  throughout  the  long  months  of 
the  dormant  season  to  dissolve  from  the  soil  such  materials 
as  will  be  of  value  in  plant-growth.  Such  soil  solution  is 
of  tremendous  value  in  establishing  the  young  plant  dur- 


TIME  OF  IRRIGATION  177 

ing  the  earlier  periods  of  growth.  Water  stored  in  the 
soil  at  the  time  of  planting  is  invariably  more  valuable, 
unit  for  unit,  than  water  applied  directly  at  the  time  of, 
or  immediately  after  planting. 

Fall  irrigation  may  be  applied  to  bare  lands  at  any 
time  after  harvest.  The  common  practice  is  to  apply  the 
water  as  soon  as  may  be  convenient  after  harvest  without 
previous  plowing,  and  to  allow  the  soil  to  remain  unplowed 
until  the  following  spring.  Another  practice  is  to  plow 
soon  after  harvest  and  then  to  apply  water.  When  the 
soil  "washes"  easily,  this  latter  practice  is  not  always 
successful;  moreover,  plowed  land  is  irrigated  with  diffi- 
culty. The  structure  of  some  soils  is  easily  injured  by 
the  work  of  making  the  water  cover  the  plowed  land,  thus 
affecting  the  crop  of  the  following  year.  On  orchards,  fall 
irrigation  should  not  be  applied  too  early.  The  soil 
should  be  allowed  to  become  dry  in  the  early  fall,  so  that 
the  trees  may  ripen  their  wood  for  the  winter's  rest. 
Then  fall  irrigation  may  be  applied  in  safety.  If  water  is 
applied  to  trees  before  growth  has  ceased,  a  late  new 
growth  is  started,  which  usually  results  in  winter-killing. 
Naturally,  this  applies  only  to  deciduous  trees.  Citrus 
trees  are  irrigated  during  the  whole  year,  if  necessary. 

Generally,  when  fall  irrigation  is  applied  late  enough 
it  results  only  in  good.  Lands  are  not  ordinarily  culti- 
vated after  fall  irrigations,  because,  over  the  larger  part 
of  the  irrigated  territory,  the  fall  rains  usually  leave  the 
top  soil  in  a  condition  to  be  puddled  if  subjected  to  tillage. 
However,  a  soil  that  has  been  fall-irrigated  should  be 
carefully  cultivated  in  the  spring,  just  as  soon  as  the  top 
soil  is  in  the  proper  condition.  It  is  never  wise  to  use 
tillage  implements  on  soils  that  are  too  wet.  Early  spring 
cultivation  always  means  cultivation  performed  on  a 
L 


178  IRRIGATION  PRACTICE 

soil  sufficiently  dry  to  support  the  tools  without  danger 
to  the  soil  structure. 

Fall  irrigation  has  been  tried  extensively  in  places 
where  the  winter  rainfall  is  light,  and  almost  invariably 
with  great  success.  Wherever  the  winter  precipitation  is 
high,  it  is  probably  unnecessary  and  possibly  inadvisa- 
ble to  practise  fall  irrigation.  Meanwhile,  the  use  of  the 
water  which  ordinarily  goes  to  waste  in  the  fall  may  be 
the  means  of  making  the  summer  flow  cover  a  larger 
area  of  land  than  would  otherwise  be  possible. 

112.  Winter  irrigation. — Winter  irrigation  means  the 
application  of  water  to  the  soil  during  the  winter  proper. 
It  is  seldom  practised  where  the  winters  are  closed  in  by 
snow  or  where  the  top  soil  is  frozen  for  weeks  or  months. 
It  is  true  that  an  unsaturated  soil,  when  frozen,  is  of  a 
granular  structure,  and  that  through  such  a  frozen  soil 
water  penetrates  to  considerable  depths.  However, 
water  applied  to  frozen  soils  stands  on  the  soil  and  often 
freezes  into  sheets  of  ice.  On  bare  soils  this  does  little 
harm  and  little  good.  A  possible  advantage  is  that  when 
the  warmer  weather  melts  the  ice  and  opens  the  soils, 
the  water  that  has  not  run  off  soaks  rapidly  into  the  soil. 
On  lands  bearing  grass  or  lucern,  great  injury  is  done 
when  sheets  of  ice  are  formed  over  the  surface  of  the  fields, 
and  winter  irrigation  should  never  be  practised  on  such 
fields  where  freezing  weather  characterizes  the  winters. 

Winter  irrigation  is  and  should  be  practised  chiefly 
where  the  winters  are  mild  and  open.  In  such  districts, 
winter  irrigation  is  really  a  later  fall  irrigation.  All  the 
arguments  in  favor  of  fall  irrigation  hold  for  such  winter 
irrigation. 

Excellent  studies  have  been  made  of  the  value  of 
winter  or  late  fall  irrigation  in  supplementing  the  rain- 


TIME  OF  IRRIGATION  179 

fall  and  increasing  the  duty  of  irrigation  water  through 
the  growing  season.  The  most  notable  of  these  studies 
was  made  in  1898  and  1899  by  McClatchie,  in  an  Arizona 
valley  where  the  annual  rainfall  averages  about  11  inches, 
and  is  so  distributed  as  to  be  heaviest  from  July  to  Sep- 
tember and  from  December  to  February.  Deciduous 
trees  shed  their  leaves  in  November;  the  buds  start  in 
February,  and  the  leaves  are  generally  out  by  the  end  of 
March.  Heavy  frosts  often  occur  in  December  and 
January.  The  orchard  used  for  the  experiments  contained 
chiefly  peaches  and  apricots  planted  in  1892.  In  1898, 
the  orchard  was  irrigated  in  September.  Then,  from* 
January  2  to  March  1,  1899,  the  orchard  received  eight 
irrigations.  It  was  then  plowed  and  harrowed.  From 
March  31  to  June  24,  1899,  no  further  irrigation  was 
applied  and  no  rain  fell  during  that  tune.  In  spite  of  the 
lack  of  irrigation  the  growth  of  the  trees  and  the  yield  of 
fruit  were  excellent.  On  December  16,  1899,  the  winter 
irrigations  began  again  and  3  acre-feet  of  water  were  ap- 
plied between  that  date  and  March  5,  1900.  During  the  fol- 
lowing eight  months  no  irrigation  water  was  applied,  and 
the  rainfall  during  that  period  was  only  about  2%  inches, 
distributed  among  five  rains.  At  the  end  of  the  eight 
months  the  trees  were  in  fine  condition  and  the  yield  of 
fruit  was  excellent.  The  season  was  the  driest  and  hot- 
test on  the  records  of  the  state. 

This  classical  experiment  demonstrates  conclusively 
the  high  crop-producing  value  of  fall  and  winter  irriga- 
tion, correctly  applied  in  districts  where  such  irrigation 
is  at  all  practical.  It  reemphasizes  also  the  doctrine  that, 
when  the  soil  is  used  as  a  storage  reservoir,  it  is  not  neces- 
sary that  much  water  be  added  during  the  growing  sea- 
son of  the  crop. 


180  IRRIGATION  PRACTICE 

McClatchie  observed  that,  as  a  result  of  heavy  win- 
ter irrigations,  the  tree  roots  grew  while  there  was  no 
visible  growth  above  the  ground.  The  strengthened  roots 
then  made  possible  rather  rapid  growth  above  ground  at 
a  later  period.  Roots  were  found  plentifully  to  a  depth 
of  16  feet  and  one  was  followed  to  a  depth  of  20  feet. 
Available  moisture  was  observed  to  a  depth  of  20  to  25 
feet.  The  major  use  of  water  by  the  trees  was  in  the 
spring  and  early  summer.  In  the  later  summer  the  trees 
were  somewhat  sluggish  so  far  as  the  use  of  water  was 
concerned.  As  a  result  of  his  investigations,  McClatchie 
advised  the  use  of  winter  irrigation,  and  not  to  exceed 
one  summer  irrigation,  for  the  successful  production  of 
fruit  in  that  section  of  Arizona. 

It  must  not  be  believed,  however,  that  under  fall  and 
winter  irrigation  plants  are  given  less  moisture  than  when 
the  water  is  added  in  summer.  More  likely  the  liberal 
use  of  water  in  fall  and  winter,  when  few  farmers  use  it, 
means  that  really  more  water  is  thus  used  for  the  produc- 
tion of  dry  matter.  In  the  experiment  above  cited,  it  was 
found  that  approximately  48  inches  of  water  were  received 
throughout  the  season.  This  was  used  by  the  orchard 
proper,  by  the  cover-crop  for  the  maintenance  of  soil 
fertility,  and  by  evaporation.  Whether  in  winter  or  sum- 
mer, water  should  be  used  sparingly. 

Winter  and  fall  irrigations  are  two  excellent  methods 
whereby  the  waters  which  now  largely  go  to  waste  may 
be  so  conserved  as  to  increase  the  duty  of  the  summer 
flow.  In  time,  as  more  reservoirs  are  built  arid  all  the 
fall  and  winter  waters  are  held  back  in  these  reservoirs, 
fall  and  winter  irrigation  will  not  be  so  important;  but 
even  under  these  future  ideal  conditions,  it  may  be  found 
desirable  to  irrigate  the  soil  in  the  fall,  so  that,  in  the 


TIME  OF  IRRIGATION  181 

spring,  there  may  be  an  abundance  of  water,  heavily 
charged  with  the  valuable  constituents  of  the  soil,  for 
the  use  of  the  young  plant. 

113.  Early  spring  irrigation. — This  refers  to  irriga- 
tion made  soon  after  the  winter  breaks,  either  before  or 
after  planting,  but  nearly  always  before  the  plant  is  really 
in  need  of  additional  water.  When  spring  appears,  the 
melting  mountain  snows  increase  greatly  the  river  flow, 
culminating  in  the  period  of  high  water  and  spring  floods. 
Unless  reservoir  provisions  are  made  these  great  quan- 
tities of  water  flow  away  unused  and  it  is  an  increasingly 
important  question  whether  this  spring  flow  may  be 
diverted  profitably  upon  cultivated  lands. 

If  the  soil  has  been  well  -filled  with  water  during  fall 
and  winter,  either  by  late  irrigation  or  by  heavy  winter 
precipitation,  it  is  probably  useless  to  expect  that  spring 
irrigations  will  benefit  crops.  The  early  application  of 
water  may  rather  be  detrimental  in  such  places,  as  it 
tends  to  wash  down,  beyond  the  reach  of  plant  roots,  the 
rich  soil  solution  formed  during  the  winter. 

On  the  other  hand,  wherever  the  winters  are  dry,  or 
where  fall  and  winter  irrigation  cannot  well  be  practised, 
the  application  of  water  in  the  early  spring  may  be  bene- 
ficial in  stimulating  early  crop-growth.  In  fact,  in  local- 
ities where  the  soil  in  spring  is  in  a  condition  too  dry 
for  germination,  it  is  indispensable  that  water  be  applied 
to  the  soil  about  the  time  of  planting,  if  any  crop  at  all 
is  to  be  obtained.  In  such  districts,  water  is  often  applied 
to  the  soil  some  time  before  the  planting  season.  After 
the  water  has  distributed  itself  throughout  the  soil,  the 
top  soil  is  loosened  to  prevent  evaporation  and  to  furnish 
a  good  seed-bed.  Usually,  however,  the  seed  is  sown  in 
the  relatively  dry  soil  and  a  rather  heavy  irrigation  is 


182  IRRIGATION  PRACTICE 

applied  afterward.  In  either  case,  germination  is 
encouraged. 

Our  present  knowledge  leads  to  the  belief  that  spring 
irrigation  should  be  practised  only  where  it  is  absolutely 
indispensable.  The  value  of  early  irrigation  depends 
upon  the  quantity  of  water  in  the  soil  in  the  early  spring. 
It  is  much  better,  wherever  conditions  permit,  to  irrigate 
in  the  fall,  and  to  conserve  in  the  soil  as  much  as  possible 
of  the  natural  precipitation,  so  that  the  seed  may  be 
planted  without  irrigation  and  the  first  irrigation  may  be 
postponed  until  early  growth  is  well  started,  and  late 
spring  or  early  summer  weather  has  set  in. 

This  matter  was  tried  out  at  the  Utah  Station  with  the 
result  that  the  longer  the  spring  irrigation  was  postponed, 
the  more  valuable  it  became  in  increasing  the  crop-yield. 
Under  the  prevailing  conditions,  there  was  a  liberal 
fall,  winter  and  early  spring  precipitation,  so  that  at  plant- 
ing time  the  soils  were  usually  saturated  with  water.  To 
irrigate  such  soils  does  little  good,  and  possibly  results 
in  harm.  Only  where  germination  will  be  delayed  or  be 
incomplete  without  irrigation  should  the  early  applica- 
tion of  water  be  practised.  It  is  of  prime  importance,  for 
obtaining  the  best  results,  that  the  soil  be  well  filled  with 
moisture  at  the  time  of  planting. 

114.  Irrigation  during  growth. — The  time  to  irrigate 
crops  during  their  growth  should  measurably  determine 
the  rotation  of  water  from  irrigation  systems  and  it  bears, 
therefore,  directly  upon  the  question  of  canal  manage- 
ment. 

In  the  spring,  when  the  root-system  is  being  developed, 
the  growth  above  ground  is  slow.  With  each  day,  however, 
the  rate  of  growth  increases,  until  buds  and  flowers 
appear.  At  that  time  the  rate  of  plant-growth  is  most 


TIME  OF  IRRIGATION  183 

rapid;  and  this  rapid  growth,  or  increase  in  weight,  con- 
tinues during  the  whole  time  of  early  flowering.  When 
seed-formation  begins,  the  rate  of  growth  diminishes; 
and  after  the  seeds  have  been  formed,  it  is  even  smaller 
than  in  the  earlier  stages. 

The  water  transpired  by  crops  is  generally,  though 
not  always,  hi  proportion  to  the  rate  of  growth.  Water 
lost  by  evaporation  from  the  soil  increases  and  decreases 
largely  in  the  same  proportion,  because  the  time,  tem- 
perature and  other  conditions  that  determine  the  rate  of 
plant-growth  also  determine  the  rate  of  direct  evaporation. 

Such  a  coincident  variation  would  mean  that  little 
water  needs  be  applied  in  the  earlier  periods  of  plant- 
growth,  but  that,  as  the  rate  of  growth  increases,  the  rate 
of  adding  water  must  be  increased  until  the  period  of 
seed-formation  approaches,  when  the  supply  may  again 
be  diminished.  In  practice,  it  is  exceedingly  difficult  even 
to  approximate  this  ideal  system  of  irrigation,  for  the 
stream  flow  in  most  localities  decreases  rapidly  from  early 
spring  until  the  time  of  maximum  water  needs  is  reached. 
At  that  time  of  high  requirements  and  low  supply  it  is 
difficult  for  the  farmer  to  supply  his  crops  with  the  best 
quantity  of  water  at  the  right  time.  Under  reservoir  con- 
ditions, the  ideal  requirements  are  more  nearly  met. 
Nevertheless,  under  any  conditions,  the  farmer  must 
attempt,  as  nearly  as  may  be  possible,  to  give  his  crops 
most  water  at  the  time  when  the  crops  need  water  most. 
This  time,  in  turn,  depends  on  the  crops  grown  under  the 
system.  By  a  wise  diversity  of  crops,  a  small  stream  hi 
early  or  late  summer  may  be  made  to  served  a  large  area 
well. 

115.  Time  of  irrigating  short-season  crops. — Wheat 
and  the  other  small  grains,  peas,  beans  and  similar  short- 


184  IRRIGATION  PRACTICE 

season  crops,  after  having  been  planted  in  a  soil  well 
filled  with  moisture,  should  be  allowed  to  grow  as  long  as 
possible  without  irrigation.  The  early  irrigation  of  such 
crops  is  only  slightly  advantageous,  and  the  results 
seldom  pay  for  the  labor  and  cost  of  water.  By  post- 
poning the  first  irrigation,  the  root-system  may  be  more 
fully  developed,  so  that  the  best  use  may  be  made  of  the 
water  when  it  is  applied.  Such  crops,  grown  for  seed, 
seldom  need  irrigation  before  the  time  of  flowering  or 
seed-formation,  when  one  or  two  moderate  irrigations 
may  be  applied  with  decided  advantage. 
•  At  the  Utah  Station  it  was  found  that,  when  a  given 
quantity  of  water  was  used,  the  total  weight  of  the  crop 
was  not  greatly  affected  by  varying  the  time  of  irrigation; 
the  effects  were  felt  in  the  yields  of  grain  produced.  When 
irrigation  was  performed  early,  before  flowering,  more 
straw  and  less  seed  were  produced;  when  irrigation  came 
late,  less  straw  and  more  seed  resulted.  The  sum  of  straw 
and  seed  was,  in  both  cases,  practically  the  same.  That 
is,  late  irrigations  make  possible  the  transfer  of  nutritive 
materials  from  the  roots  and  stalks  to  the  heads,  there  to 
be  permanently  elaborated  into  seed  materials. 

After  the  seeds  are  well  formed  there  is  seldom  any 
advantage  in  irrigation.  Certain  varieties  of  grain,  peas 
and  beans  have  an  extended  growing  season,  and  to  such 
it  may  be  necessary  to  apply  water  some  time  before 
flowering,  and  perhaps  once  after  seed-formation  is  well 
under  way.  Even  to  the  crops  that  mature  early,  it  may 
often  be  profitable  to  add  water  at  the  time  the  seeds 
are  forming  most  rapidly,  for  it  may  help  fill  them  more 
completely. 

116.  Time  of  irrigating  long-season  crops. — Sugar 
beets,  potatoes,  corn  and  similar  crops  should  also  be 


TIME  OF  IRRIGATION  185 

planted  in  well-saturated  soil.  The  first  irrigation  should 
be  postponed,  for  the  reasons  already  given,  until  the 
plants  really  show  need  of  water.  From  the  time  of  the 
first  irrigation,  water  must  be  applied  to  these  long- 
growing  crops  at  regular  intervals  throughout  the  grow- 
ing season.  Sugar  beets,  carrots,  corn  and  like  crops, 
planted  usually  in  May,  need  the  greater  quantity  of 
water  in  July  and  first  half  of  August.  From  the  first  of 
September  and  during  autumn,  little,  if  any,  water  should 
be  applied,  even  if  the  harvest  does  nob  occur  until  October 
or  November.  Sugar  beets  are  seldom  benefited  by  irri- 
gation after  the  first  of  September. 

Under  the  conditions  of  the  inter-mountain  coun- 
try and  on  deep  clayey  or  loamy  soils,  5  inches  of  water  is  a 
fairly  large  single  application.  An  irrigation  of  this 
degree  every  two  or  three  weeks  throughout  the  season, 
from  the  time  of  the  first  irrigation  until  the  first  week  in 
September,  is  quite  sufficient  to  maintain  the  soil  in  a 
first-class  condition  for  the  needs  of  beets  and  other  long- 
season  crops.  Usually,  a  much  smaller  quantity  of  water 
at  each  irrigation  will  suffice  to  produce  a  bountiful  har- 
vest of  root  crops.  It  is  doubtful,  however,  if  more  than 
three  weeks  should  elapse  between  irrigations,  where 
water  is  fairly  abundant,  for  if  the  soil  dries  out  too  much 
the  plant  may  be  injured  permanently.  When  15  acre- 
inches  are  applied  throughout  the  season  it  is  well  to 
apply  them  hi  four  or  five  irrigations.  The  deeper  the 
soil,  and  the  more  thorough  the  surface-cultivation,  the 
fewer  need  be  the  applications.  During  the  hot  season,  they 
will  naturally  be  closer  together  than  in  the  early  or  late 
summer.  In  one  series  of  experiments,  the  highest  yield 
of  carrots,  a  long-season  crop,  was  obtained  with  seven 
irrigations;  the  highest  yield  of  sugar  beets  was  obtained 


186  IRRIGATION  PRACTICE 

with  six  irrigations.  Excellent  crops  of  carrots  were,  how- 
ever, obtained  with  four  irrigations,  and  of  sugar  beets, 
with  only  two  irrigations.  Each  district  must  work  out 
the  problem  for  itself,  keeping  well  in  mind  that  root 
crops  must  be  made  to  wait  as  long  as  possible  for  the 
first  irrigation  and  that  thereafter,  until  early  fall,  they 
should  receive  rather  regular  irrigations. 

Lucern,  or  alfalfa,  should  be  watered  with  reference 
to  the  number  and  times  of  cuttings.  Over  the  irrigated 
district  three  cuttings  of  lucern  are  ordinarily  obtained 
annually.  The  first  irrigation  should  be  applied  when  the 
crop  goes  into  flower,  which  is  the  time  of  the  greatest 
rate  of  growth.  The  next  irrigation  may  be  applied  just 
before  or  after  the  first  cutting.  This  second  irrigation 
is  intended,  primarily,  for  the  use  of  the  second  crop,  and 
its  chief  effect  is  to  stimulate  the  early  growth  of  the 
second  cutting.  It  matters  little  whether  the  crop  be  irri- 
gated immediately  before  or  after  the  cutting.  It  is  pos- 
sible that  an  irrigation  before  cutting  permits  the  water  to 
be  distributed  more  thoroughly  in  the  soil,  before  the 
growth  of  the  second  cutting  begins.  On  the  other  hand, 
the  longer  the  interval  between  the  irrigation  and  the  cut- 
ting of  the  first  crop,  the  larger  the  loss  by  evaporation. 
Each  cutting  of  lucern  could  well  receive  an  irrigation  at 
the  time  of  flowering  and  another  at  the  time  of  cutting, 
excepting  the  third  crop,  which  is  usually  cut  so  late  as 
to  require  no  further  irrigation,  unless  it  be  the  fall  irri- 
gation which  is  practised  for  the  benefit  of  next  crop. 

Hay  crops  that  yield  only  one  cutting  a  year  should 
be  treated  very  much  as  is  the  first  cutting  of  lucern. 
The  one  irrigation  should  be  applied  at  the  time  of  flow- 
ering or  seed  time.  If  the  aftermath  is  to  be  used,  one  or 
more  small  applications  may  be  applied  throughout  the 


TIME  OF  IRRIGATION  187 

season,  to  maintain. the  late  growth.  Pastures  which  in 
the  irrigated  section  are  maintained  during  the  whole 
season  require  small  but  regular  applications  of  water 
from  spring  to  fall. 

The  time  to  apply  water  to  fruit  trees  depends  on 
both  fruit-  and  bud-formation.  The  fruit-buds  are  formed 
the  year  preceding  the  bearing  of  the  fruit.  At  the  time 
that  these  are  formed,  usually  in  late  midsummer,  when 
the  fruit  is  still  small  and  immature,  the  crop  should  be 
plentifully  supplied  with  water.  Fruit  trees  require  a 
moderate  amount  of  water  in  the  spring  and  early  summer 
with  an  increasing  quantity  as  the  summer  advances  and 
the  fruit  develops.  Late  fall  irrigation  of  orchards,  after 
the  season's  wood  has  ripened,  is  beneficial  to  the  succeed- 
ing crop,  except  in  places  where  the  winter  precipitation 
is  very  heavy. 

117.  Night  vs.  day  irrigation. — Water  is  usually 
allowed  to  run  through  the  canals  with  equal  volume  by 
day  and  by  night.  The  night  water,  so  far  as  is  known,  is 
quite  as  valuable  as  the  day  water  in  crop-production. 
However,  night  irrigation  naturally  is  more  difficult  to 
perform.  Sanborn  and  others  have  experimented  on  the 
relative  value  of  night  and  day  irrigation.  Their  results 
lead  to  the  conclusion  that  there  is  no  material  difference 
in  results  between  night  and  day  irrigation.  Where  the 
water  supply  is  small,  it  must  be  husbanded  carefully, 
and  the  farmer  then  uses  it  both  day  and  night. 

REFERENCES 

HARRIS,  F.  S.  Studies  in  Soil  Moisture  and  Fertility. 

HARRIS,  F.  S.  Long  versus  Short  Periods  of  Transpiration  in  Plants 
Used  as  Indicators  of  Soil  Fertility.  Proceedings  of  the  Ameri- 
can Society  of  Agronomy,  Vol.  II,  p.  93  (1910). 


188  IRRIGATION  PRACTICE 

McCLATCHiE,  ALFRED  J.   Winter  Irrigation  of  Deciduous  Orchards. 

Arizona  Experiment  Station,  Bulletin  No.  37  (1901) ;  also  United 

States  Department  of  Agriculture,  Farmers'  Bulletin  No.  144 

(1901). 
MCDOWELL,    R.    H.     Irrigation.     Nevada    Experiment    Station, 

Bulletin  No.  25  (1894). 
RICHMAN,  E.  S.   United  States  Horticultural  Department  Bulletin 

No.  20  (1893). 
SANBORN,  J.  W.    Night  versus  Day  Irrigation.    Utah  Experiment 

Station,  Bulletin  No.  21  (1893). 
WELCH,   J.   S.     Irrigation   Practice.     Idaho  Experiment  Station, 

Bulletin  No.  74  (1914). 
WIDTSOE,  J.  A.,  and  MERRILL,  L.  A.    Methods  for  Increasing  the 

Crop-Producing  Power  of  Irrigation  Water.    Utah  Experiment 

Station,  Bulletin  No.  118  (1912). 


CHAPTER  X 
THE  METHOD  OF  IRRIGATION 

THE  method  of  irrigation  determines  greatly  the  duty 
of  water  and  the  profitableness  of  irrigation.  The  con- 
siderable labor  which  always  attends  the  application  of 
water  to  land  is  one  of  the  big  charges  to  be  made  against 
irrigation,  and  one  that  must  be  made  as  low  as  possible. 
Besides,  the  method  of  irrigation  frequently  affects, 
directly,  the  degree  to  which  plants  may  use  the  water 
applied. 

There  are  only  two  general  methods  of  applying  irri- 
gation water;  first,  irrigation  above  ground  and,  second, 
irrigation  below  ground.  Each  of  the  two  methods  appears 
under  several  variations  and  possesses  a  special  advantage. 
In  practice,  the  method  of  applying  water  above  ground 
is  the  only  one  in  general  use. 

118.  Sub-surface  irrigation. — The  application  of 
irrigation  water  from  below,  or  sub-surface  irrigation,  has 
the  advantage  that  water  so  applied  is  not  subjected  to 
such  direct  evaporation  from  the  surface  as  of  necessity 
accompanies  surface  irrigation.  When  water  is  scarce, 
it  is  especially  of  great  importance  to  reduce  such  evapora- 
tion. For  this  purpose,  sub-irrigation  seems  to  be  the 
method  that  should  be  employed. 

It  should,  however,  be  kept  in  mind  that  the  suc- 
cessive wetting  and  drying  of  the  top  soil,  which  accom- 
panies surface  irrigation,  benefits  crops  and  enables  them 
to  produce  dry  matter  with  least  water,  and  often  this 

(189) 


190  IRRIGATION  PRACTICE 

benefit  overshadows  the  loss  by  evaporation.  In  the 
Utah  work,  some  attention  was  given  to  the  effect  of  irri- 
gation above  ground  with  respect  to  the  transpiration 
ratio.  In  every  case,  much  larger  quantities  of  water 
were  evaporated  when  the  water  was  applied  to  the  sur- 
face of  the  soil  than  when  applied  by  sub-irrigation,  but  a 
pound  of  water  applied  to  the  surface  produced  as  much 
dry  matter  as  when  applied  below  the  surface.  It  may  be 
that  the  value  of  sub-irrigation  has  been  considerably 
exaggerated  because  the  diminution  of  evaporation  only 
has  been  considered. 

Aside  from  these  theoretical  considerations,  sub-irri- 
gation has  not  received  wide  acceptance,  due  to  certain 
intrinsic  difficulties,  which  seem  insurmountable.  Sub- 
irrigation  implies  underground  water  channels,  opened 
at  various  places  for  the  escape  of  water  to  the  crop. 
These  underground  channels  are  usually  pipes  of  iron  or 
concrete  or  wood.  Machines  are  on  the  market  which, 
as  they  move  along,  open  the  soil  to  the  requisite  depth 
and  at  the  same  time  lay  a  concrete  pipe  of  the  desired 
dimension.  The  cost  of  installing  such  a  system  is  very 
great  and  adds  immensely  to  the  initial  cost  of  irrigation. 
With  the  present  prices  of  land,  water  and  crops,  it  is  not 
good  business  to  install  sub-irrigation  systems,  unless  it 
be  in  a  few  favored  localities  where  conditions  of  labor  and 
markets  are  just  right. 

It  may  be  urged  that  such  a  system  once  installed  and 
out  of  sight  requires  little  further  attention;  whereas  sur- 
face irrigations  require  a  large  annual  cost  for  the  upkeep 
of  ditches  and  the  actual  spreading  of  water  over  the 
land.  This  advantage  is,  however,  more  apparent  than 
real.  Leaks  are  often  sprung  in  the  underground  systems 
which  are  located  with  difficulty  and  remedied  at  large 


METHOD  OF  IRRIGATION 


191 


expense.  Still  worse,  plant  roots,  always  in  search  of 
water,  are  gradually  directed  to  the  openings  hi  the  under- 
ground pipes,  and  fill  them  so  completely  that  the  flow 
of  water  is  either  greatly  diminished,  or  entirely  stopped. 
For  this  reason  every  sub-irrigation  system  has  either  been 
abandoned  or  has  been  maintained  only  hi  spite  of  the 


CA+/AL 


FIG.  32.  Plan  of  a  sub-irrigated  farm  in  Idaho. 


great  cost  of  keeping  the  water  outlets  free  from  plant 
roots.  The  best  that  can  be  said  about  sub-irrigation  is 
that  the  method  has  not  yet  been  perfected,  and  that  it 
offers  a  fine  field  for  the  agricultural  inventor. 

One  kind  of  sub-irrigation  of  extremely  limited  appli- 
cation has  proved  successful.  In  certain  localities  are 
found  somewhat  sandy  soils,  1  to  5  feet  in  depth,  under- 
laid by  an  almost  impervious  clay.  Ditches  are  dug  at 
intervals  of  }/%  to  %  mile.  The  water  flowing  through  these 


192 


IRRIGATION  PRACTICE 


ditches  sinks  until  it  reaches  the  clay  bottom,  along  which 
it  travels  for  great  distances  within  reach  of  plant  roots. 
Some  of  the  finest  fields  in  western  America  are  supplied 
with  water  by  this  inexpensive  process  of  natural  lateral 
seepage.  Clearly,  this  method  is  so  limited  in  extent  that 


mm" 

GRAVEL  GRAVEL 

Fio.  33.  Lee's  sub-irrigation  system. 

it  deserves  only  a  passing  notice.  Yet  it  should  be  kept  in 
mind,  so  that,  whenever  the  conditions  appear  to  be 
suitable,  attempts  may  be  made  to  irrigate  crops  by 
natural  sub-irrigation.  (Figs.  32,  33.) 

Except  in  greenhouses  and  under  natural  systems,  sub- 
irrigation  may  be  eliminated  from  consideration. 


METHOD  OF  IRRIGATION  193 

119.  Surface  irrigation. — Surface  irrigation  is  the 
method  generally  adopted  hi  all  irrigated  countries. 
There  is  a  great  variety  of  methods  of  surface  irrigation, 
most  of  which  are  scarcely  worth  consideration,  because 
they  either  fail  to  recognize  the  natural  laws  underlying 
irrigation,  or  then*  cost  of  installation  is  beyond  practi- 
cability. 

The  approved  methods  of  surface  irrigation  may  be 
classified  under  two  heads:  first,  the  flooding  methodj 
second,  the  furrowing  rnethod.  Byjbhe  flooding  method, 
all  the  soil  is  covered  by  the  water  applied;  by  the  furrow- 
ingjnethod,  the  water  is  guided  in  furrows-jor-channels 
which  traverse  the  whole  field,  but  the  water  covers  only 
a  part  of  the  soil  surface.  Both  flooding  and  furrowing 
are  used  extensively  hi  all  irrigated  regions.  In  one 
locality  flooding  may  be  the  general  method;  hi  anotlier, 
furrowing.  The  adoption  of  one  or  the  other  of  these 
methods  depends  sometimes  upon  careful  trials,  but  more 
often  upon  custom  following  the  first  practices. 

The  chief  factors  determining  the  choice  between  flood- 
ing and  furrowing,  are:  (1)  the  nature  of  the  soil,  (2)  the 
contour  of  the  land,  (3)  the  head  of  the  water  stream, 
(4)  the  quantity  of  water  available,  and  (5)  the  nature  of 
the  crop. 

If  the  soil  is  light  and  "washes" — a  condition  exist- 
ing over  large  areas  of  the  irrigated  section — furrowing 
is  the  only  really  practicable  method.  On  such  soils,  the 
soil-washing  due  to  flooding  often  results  in  large  chan- 
nels, gullies  or  "washes"  being  cut  in  the  soil.  On  heavier 
soils,  flooding  may  be  practised  safely,  as  far  -as  erosion  is 
concerned.  Many  soils,  after  having  been  wetted,  bake  and 
form  a  hard  crust,  which  is  injurious  to  the  soil  and  to 
the  plant.  On  such  soils  the  furrowing  method  is  advisa- 

M 


194  IRRIGATION  PRACTICE 

ble,  for  by  that  method  only  a  part  of  the  surface  is  cov- 
ered with  water,  and  that  part  may  be  covered  with  loose 
earth  by  cultivation  soon  after  irrigation.  Other  soils, 
after  having  been  wetted,  as  they  dry,  fall  apart,  form- 
ing natural  mulches.  On  these  soils,  flooding  is  quite 
safe. 

On  relatively  level  land,  either  flooding  or  furrowing 
may  be  adopted.  Flooding  is  best  done  when  the  slope  of 
the  land  is  not  great,  especially  if  the  soil  tends  to  "wash" 
easily.  On  steeper  lands,  furrowing  must  be  employed. 
The  heavier  the  soil,  the  steeper  may  be  the  inclination; 
the  lighter  the  soil,  the  gentler  must  be  the  inclination. 
On  the  relatively  steep  slopes,  frequently  used  for  orchards, 
furrowing,  alone,  is  employed,  and  the  sharp  descents  are 
overcome  by  carrying  the  furrows  back  and  forth  around 
the 'slopes  with  any  desired  fall.  While  no  definite  rule 
can  be  laid  down  as  to  the  permissible  inclination  of 
lands  under  irrigation,  yet  a  farmer  soon  learns  by  experi- 
ence the  practice  best  suited  to  his  land.  Farm  irriga- 
tion systems  should  be  laid  out  with  reference  to  the  con- 
tour of  the  land  and,  therefore,  the  irrigation  farmer 
should  first  secure  contour  maps  of  the  land  which  he  in- 
tends to  bring  under  irrigation. 

By  the  "head"  is  understood  the  volume  of  water 
supplied  to  the  unit  of  time.  Under  some  systems  of  canal 
management,  farmers  are  given  large  streams  of  water 
for  short  times;  under  other  systems,  small  streams  are 
available  for  longer  periods.  The  total  quantity  of  water, 
at  the  end  of  the  period,  may  in  either  case  be  practically 
the  same.  A  high  head  of  water  pushes  rapidly  over  the 
land.  Loose,  sandy  soils  that  absorb  water  rapidly  must 
be  irrigated  with  a  high  head  of  water,  especially  under 
the  flooding  method,  or  the  water  may  all  be  drawn  into 


METHOD  OF  IRRIGATION  195 

the  soil,  before  the  lower  end  of  the  field  is  reached.  Under 
the  flooding  method,  a  high  head  of  water  may  be  used  on 
nearly  all  soils,  but  a  low  head  is  suitable  only  for  heavier 
soils.  It  follows  that  the  furrowing  method  is  best  adapted 
where  the  head  of  water  is  low;  the  flooding  method  where 
the  head  is  high.  This  deduction  has  found  practical 
expression  over  the  whole  irrigated  area. 

If  irrigation  water  is  abundant,  and  a  high  head  may 
consequently  be  secured,  the  flooding  method  is  usually 
employed.  If  water  is  scarce,  the  main  consideration  is 
to  make  the  total  supply  cover  the  largest  number  of 
acres,  and  the  furrowing  method  is  ordinarily  employed, 
since  by  this  method  a  small  quantity  of  water  may  be 
made  to  cover  much  land.  It  has  been  shown  that  the 
productive  power  of  water  decreases  as  the  total  quantity 
applied  to  a  given  area  is  increased.  That  is,  with  each 
additional  inch  of  water,  less  dry  matter  is  produced. 
Consequently,  where  water  is  scarce,  it  is  more  profitable 
to  spread  the  small  quantity  of  water  over  a  large  area  of 
land.  To  do  this,  the  furrow  method  is  indispensable.  In 
irrigation  practice,  therefore,  although  the  reason  is  not 
always  understood,  the  furrowing  method  is  invariably 
used  wherever  the  supply  of  water  is  low. 

The  nature  of  the  crop  determines,  also,  the  method  of 
irrigation.  Some  plants  are  more  sensitive  than  others  to 
contact  with  water.  It  is  believed  by  many  that  the 
sugar  beet  is  injured  whenever  irrigation  water  is  allowed 
to  come  into  contact  with  it,  especially  if  the  day  is  hot. 
This  may  be  true  at  times,  but  this  danger  is  much  exag- 
gerated. Only  when  water  stands  against  a  plant  for 
some  time  is  injury  really  likely,  and,  then,  injury  comes 
either  when  the  water  is  so  hot  as  to  cause  sun-scald 
or  so  cold  as  to  chill  the  plant.  In  either  case,  the  process 


196 


IRRIGATION  PRACTICE 


of  growth  is  retarded.    Much  work  yet  needs  to  be  done 

on  this  subject. 

/  The  various  modifications  of  the  flooding  method 
/  may  be  grouped  into  (1)  flooding  open  fields,  and  (2)  flood- 
/  ing  closed  fields.  Open  fields  are  those  not  surrounded  by 

levees.    Closed  fields  are  those  completely  surrounded  by 

levees,    making   a    compartment    into    which    water   is 

admitted. 

120.  Permanent    ditches. — A    permanent    system    of 

ditches,  having  in  view  immediate  and  probably  future 


FIG.  34.  A  permanent  ditch  in  an  orange  grove  (Redlands). 


needs,  should  be  constructed  on  every  farm,  to  connect 
the  canal  with  the  field  to  be  irrigated.  The  ditches  should 
be  placed  so  as  to  interfere  as  little  as  possible  with  regu- 
lar agricultural  operations,  and  they  should  conform 
either  to  the  contour  of  the  land,  or  to  some  well  defined 
plan  for  dividing  the  farm  into  fields.  The  laying  out  and 


METHOD  OF  IRRIGATION 


197 


construction  of  permanent  ditches  is  the  first  big  thing  in 
irrigation  agriculture.  Great  waste  has  occurred  and  is 
occurring  because  of  carelessness  in  this  matter. 

The  ditches,  once  decided  upon,  should  be  built  in  a 
permanent  fashion,   so  that  they  will  not  need  to  be 


I 
..!• 

I 


-c/?oss  otrcH 


\ 

I 

•t • 

I 
I 


I'' 


I 

I. 


..—-"'" 


j 


rm 

m 


., j - 

_- H 

^..1." **  **-" 


Ii      I"""' 

^5SSS. 


Fia.  35.  Plan  of  field-ditch  irrigation. 

repaired  greatly  from  year  to  year.  In  the  older  and  more 
prosperous  irrigated  sections,  ditches  are  often  made  of 
concrete  and  are  consequently  practically  indestructible. 
The  best  illustration  of  this  kind  of  ditch  is  found  in  Cali- 
fornia, notably  in  the  Riverside  district,  where  the  orange 
groves  require  that  water  be  made  to  do  its  highest  duty. 


198 


IRRIGATION  PRACTICE 


••  J^?^rou^- 


1'AAV'? 


FIG.  36.  Flooding  from  ditches  running  down  the  steepest  slope. 

The  main  permanent  ditches  if  made  of  concrete,  are  fre- 
quently put  underground,  out  of  sight  and  out  of  the  way. 
The  water  is  allowed  to  escape  through  stand-pipes  into 
the  temporary  ditches  of  the  farm.  The  beauty  and  often 
the  prosperity  of  the  irrigated  farm  depend  upon  the 
permanent  ditches.  (Fig.  34.) 

121.  Field-ditch  or  field-lateral  method. — This  method, 


FIG.  37.  Flooding  from  field  ditch. 


METHOD  OF  IRRIGATION 


199 


which  is  the  mostjargely  used  method  of^ogen_field-flood- 
ing,  is  especially  adapted  to  level  lands  with  gentle  slopes. 
By  this  method,  the  water  is  taken  out  of  the  main  ditches 
at  various  intervals,  and  as  it jflows  _oyer  thejjejdj  is  dis- 
tributed property"  over  the  field  by  small  temporary 
ditches  or  furrows.  These  small  laterals  follow  the  high 


BB 

FIG.  38.  Flooding  with  aid  of  canvas  dam. 

places  of  the  field,  and  the  water  overflowing  their  banks 
covers  the  field. 

For  instance,  wheat  is  planted  in  the  usual  way,  with- 
out reference  to  the  field  ditches  which  are  made  after 
the  wheat  has  germinated  and  is  a  few  inches  high.  The 
small  laterals  are  made  with  a  small  horse-plow  made  for 
the  purpose,  or  they  are  made  by  the  irrigator  with  a  hoe. 
The  field  ditches  of  lucern  and  similar  permanent  crops, 
once  made,  remain  from  year  to  year,  except  that  they 
may  be  deepened  a  little  from  season  to  season.  These 


200 


IRRIGATION  PRACTICE 


FIG.  39.  Laterals  made  in  field  and  dammed  with  small   piles  of   manure  for 
next  year's  irrigation. 

field  ditches,  however,  whether  in  wheat  or  alfalfa,  are 
so  small  as  to  be  of  no  hindrance  in  the  cultural  operations 
of  the  farm. 

The  essential  feature  of  this  method  of  irrigation  is 
the  guiding  of  the  water  over  the  land  through  numberless 
furrows  or  small  ditches.  This  is  hard  and  slow  work. 
One  man  can  cover  daily  only  a  few  acres  at  most  by  this 
method.  The  greatest  advantage  of  the  field-ditch  method 


METHOD  OF  IRRIGATION 


201 


is  that  the  first  cost  of  preparing  the  land  for  irrigation  is 
small;  the  top  soil  is  not  disturbed,  and  the  field  is  not 
cut  up  by  levees  that  make  ordinary  farming  operations 
difficult.  The  disadvantages  are  that  the  necessary 
field  labor  is  hard;  the  field  ditches  must  be  made  over 
from  year  to  year;  and,  finally,  it  is  difficult  to  secure 
an  even  distribution.  It  is  clear,  however,  from  the 
great  extension  of  this  method  that  the  advantages  over- 
shadow the  disadvantages.  This  is  the  method  employed 
by  the  Mormon  pioneers  when  they  founded  irrigation 
in  the  Salt  Lake  Valley  and  is  still  one  of  the  safest  methods 
of  irrigation  in  Utah,  Idaho,  Wyoming,  (Colorado  and  some 
of  the  other  irrigated  states.  Practically  all  manner  of 
crops,  except  those  planted  and  cultivated  in  rows,  can 
be  irrigated  by  this  method.  In  spite  of  its  disadvantages, 
immense  yields,  the  largest  on  record,  have  been  secured 
by  this  method  of  irrigation.  (Figs.  35-39.) 


- 

— 

Dike 

3 
'6 

T3 

^_           J 
1? 

1? 

Dike 

£ 

— 

i 

__J 

Fia.  40.  Plan  for  border  irrigation. 

202  IRRIGATION  PRACTICE 

122.  The   border   method. — The   border   method   of 
irrigation  is  an  open-field  method.    By  this  method  the 
field  is  divided  by  low  flat  ridges  of  earth  into  long  narrow 
strips,  the  lower  ends  of  which  are  open.   The  ridges  are 
spaced  about  50  feet  apart  and  are  frequently  800  feet 
long.  Water  is  guided  over  the  land  by  field  ditches.  This 
modification  of  the  field-ditch  method  has  for  its  purpose 
the  better  control  of  the  water.    The  ridges  prevent  the 
water  from  spreading  beyond  the  distance  determined 

between  the  ridges. 
This  enables  the 
irrigator  to  watch  the 
water  more  closely. 
When  the  .water 
reaches  the  lower  end 
of  the  strip,  it  may  be 

FIG.  41.  Border  method  of  irrigation. 

shut  off  and  another 

strrp  attacked.  The  advantages  and  disadvantages  are, 
practically,  those  explained  for  the  field-ditch  method, 
except  that  the  lateral  ridges  make  the  handling  of  the 
water  somewhat  easier.  In  cultural  operations  the  ridges 
are  in  the  way.  (Figs.  40,  41.) 

123.  The  check  method. — This  is  the  most  important 
of  the  closed -field  variation  of  applying  water  by  the 
flooding  method.    The  field  is  laid  off  into  compartments 
or  checks  wholly  surrounded  by  levees.    The  water  is 
admitted  at  the  upper  end  and  completely  fills  the  com- 
partments until,  hi  many  cases,  it  overflows  at  the  lowest 
point  of  the  levee.    This  method  of  irrigation  has  been 
practised    from    the    earliest    antiquity.     The    irrigated 
countries  of  Europe,  Asia  and  Africa  employ  this  method 
very  largely. 

Evidently  it  is  adapted  only  to  comparatively  level 


204 


IRRIGATION  PRACTICE 


land;  if  the  slope  is  great,  the  lower  levee  must  be  made 
too  high  for  practical  purposes.  A  large  head  is  always 
necessary;  for,  if  the  head  is  small,  the  land,  especially  if 
sandy,  is  likely  to  absorb  the  water  so  fast  at  the  upper 


FIG.  43.  Rectangular  check  method  of  irrigation. 

end  that  the  lower  end  receives  only  a  small  part  of  the 
water  intended  to  cover  the  whole  check.  The  flow  of 
water  should  be  from  5  to  10  second-feet  in  order  to  make 
the  method  thoroughly  successful.  In  the  older  countries, 
the  checks  are  usually  small.  In  America,  the  checks  are 
often  very  large — from  10  to  20  or  more  acres.  The 
check  method  of  irrigation,  to  be  really  successful,  must 
be  practised  with  small  checks,  at  the  most  from  1  to  3 
acres  in  area. 

The  compartments  may  be  laid  off  in  various  ways. 
If  the  land  does  not  slope  too  much,  the  whole  farm  is 
laid  off  into  square  or  rectangular  checks,  into  which  the 
water  is  admitted  in  succession.  Where  the  land  is  uneven, 
or  the  slope  steep,  the  checks  are  made  to  conform  to 
the  contour  of  the  land.  In  either  case,  water  must  be 
admitted  at  the  highest  point  and  be  brought  rapidly  into 
the  compartment  so  that  the  ground  may  be  covered 
thoroughly  and  in  a  short  time.  At  times  a  depression  is 


METHOD  OF  IRRIGATION 


205 


made  in  the  lower  levee  over  which  the  excess  of  water 
passes  into  the  next  lower  check. 

The  check  method  of  irrigation  has  some  advantages. 
Once  the  checks  or  the  levees  have  been  well  constructed, 
one  man  may  irrigate  7  to  15  acres  a  day.  The  cost  of 
preparing  the  land  for  irrigation,  after  the  first  year, 
when  the  levees  are  made,  is  very  small.  The  quantity 
of  water  applied  can  be  very  accurately  gauged  and 
evenly  distributed  by  this  method.  For  crops  such  as  rice, 
which  demand  that  the  soil  be  kept  moist  or  even  sub- 
merged for  long  periods  throughout  the  year,  the  check 
method  of  irrigation  is  indispensable.  Such  crops  are  few, 
and  the  check  method  is,  in  fact,  used  more  extensively 


Fio.  44.  Contour  check  method  of  irrigation. 

for  other  crops.  The  check  method  of  irrigation  also  has 
many  disadvantages.  The  levees  cost  from  $7  to  $20  an 
acre,  under  American  conditions,  where  the  compartments 
are  large.  The  cultural  operations  of  the  farm  are  delayed 
and  the  machinery  damaged  by  passing  back  and  forth 
over  the  high  levees.  In  any  case,  they  are  in  the  way 


206  IRRIGATION  PRACTICE 

and  are  a  disagreeable  feature  on  the  farm.  The  farmer 
finds  it  difficult  to  change  to  new  and  possibly  better 
cropping  systems,  without  going  to  the  large  expense  of 
leveling  the  old  levees  and  throwing  up  new  ones.  If 
the  soil  bakes,  this  method  should  not  be  employed  at  all, 
since  water  covers,  for  some  time,  the  whole  area.  It  is 
impossible  by  this  method  to  keep  water  from  touching 


FIG.  45.  Filling  checks  with  detachable  pipes. 

the  crop.  The  relatively  large  quantities  of  water  that 
must  be  used  by  this  method  tend  to  keep  the  roots  very 
near  the  surface,  and  the  crop  will  be  more  intensely 
affected  by  adverse  conditions  of  heat  or  cold. 

The  check  method  is,  next  to  the  field-ditch  method, 
the  most  important  method  of  applying  water  to  crops; 
|yet,  its  disadvantages  overshadow  its  advantages,  and  it 
is  a  method  which,  in  all  probability,  will  gradually  pass 


METHOD  OF  IRRIGATION 


207 


FIG.  46.  Orchard  irrigation  by  basin  method. 


out  of  general  use,  and  be  retained  only  where  crop,  soil 
or  other  conditions  make  it  necessary.    (Figs.  42-45.) 

124.  The  basin  method. — The  basin. method  is  prac- 
tically identical 
with  the  check 
method.  It  re- 
fers to  checks  in 
orchards  with  a 
tree  in  the  cen- 
ter of  each,  and 
with  temporary 
levees.  Earth  is 
heaped  around 
the  tree  trunks 
to  keep  the  water 
away  from  the 
bark.  This  method  is  used  especially  in  mild  climates 
where  fall  or  winter  irrigation  is  practised.  The  use  of 
this  method  is  also  rapidly  decreasing,  and  is  likely  soon 
to  pass  out  of  practice.  The  advantages  and  disadvan- 
tages of  this  method  of  irrigation  are  those  discussed 
under  the  check  method.  (Figs.  46-48.)  ^\^ 

^.-c^;-:-:^-^^-^^.**-,^          125rThe  furrow 
'* -.7 '*    » Vi,r~il'L~^il.jjl iisr JfC' «L tuml     method. — In    this 

method  of  irrigation, 
small  furrows  leading 
from  the  supply  ditch 
traverse  the  fields  to 
be  irrigated.  Water 
flows  down  the  fur- 
rows and  is  absorbed 
by  the  soil.  Next  to 
the  method  of  flood- 


^ 


FIG.  47.  Orchard  irrigation  by  basin  method. 


208 


IRRIGATION  PRACTICE 


ing  by  field  ditches,  this  is  the  most  common  method  of 
irrigation,  and  it  promises,  at  least  in  America,  to  super- 
sede all  other  methods. 
(Figs.  49,  50.) 

After  the  crop  has 
been  planted,  small 
furrows  leading  from 
the  supply  ditch  at 
the  head  of  the  field  are  made  to  cover  the  field  by 
some  of  the  many  kinds  of  markers  or  furrowers.  This 
process  of  furrowing  the  land  is  known  as  "marking"  or 


FIG.  48.  Grading  of  interior  of  basins  to  pre- 
vent water  from  coming  in  contact  with 
trees. 


FIG.  49.  Furrow  irrigation. 


METHOD  OF  IRRIGATION 


209 


"laying  off"  the  land.  (Fig.  52.)  The  furrows  are  made  at 
right  angles  to  the  supply  ditch,  or,  if  the  land  is  irregular 
in  contour,  they  are  made  to  follow  the  contour  lines. 
This  is  done,  especially,  in  orchards  where  trees  grow 


FIG.  50.  Furrow  irrigation  of  young  alfalfa. 

on  the  hillsides.  It  is  not  an  uncommon  sight  in  such 
districts  to  see  thirty  or  forty  furrows  filled  with  water 
zigzagging  down  a  hillside. 

The  furrows  are  made  from  year  to  year,  except  in  the 
case  of  alfalfa  and  other  perennial  crops.  Alfalfa,  when 
irrigated  by  this  method,  is  furrowed  the  first  year,  and 
the  permanent  furrows  are  only  deepened  or  cleaned  out 
from  year  to  year.  The  disadvantage  of  the  permanent 
furrows  is  that  as  the  mower  travels  across  them  the  rider 
is  shaken  up  considerably  and  the  machine  is  injured.  In 
wheat  fields,  furrows  are  laid  off  soon  after  the  wheat  is 
planted,  when  it  is  about  3  or  4  inches  high.  Fields  of 
sugar  beets,  potatoes  and  similar  crops  are  furrowed  just 
before  the  first  irrigation.  One  furrow  is  ordinarily  made 
between  every  two  rows  of  plants,  although  on  some  soils 

N 


210  IRRIGATION  PRACTICE 

the  distance  between  furrows  is  greater.  In  orchards,  the 
furrows  are  usually  made  at  the  time  of  the  first  irrigation. 
When  the  trees  are  young,  one  furrow  is  made  on  each 
side  of  each  row,  perhaps  2  feet  or  a  little  more  away  from 
the  tree.  As  the  tree  becomes  older  and  the  root-system 


Fio.  51.  One-way  furrow  irrigation. 


expands,  the  furrow  is  moved  away  from  the  tree  until,  as 
the  tree  approaches  maturity  and  more  water  is  needed, 
three  or  four  furrows  may  be  made  between  two  rows  of 
trees.  The  principle  in  spacing  the  furrows  is  that  the 
furrows  shall  be  so  close  together  that  the  water  soaking 
from  the  furrows  into  the  soil  will  meet  and  thoroughly 


METHOD  OF  IRRIGATION 


211 


saturate  the  soil  below  the  surface.  In  orchards  where 
trees  are  16  to  20  feet  apart,  one  furrow  cannot  do  this 
and  several  furrows  are  employed.  The  reason  for  using 
only  one  furrow  when  the  tree  is  young  is  that  the  roots 
have  not  spread  sufficiently  to  make  use  of  water  that 
might  be  applied  half  way  between  the  rows  of  trees;  and, 
moreover,  the  young  tree  needs  little  water.  Fewer  and 


FIG.  52.  Furrowing  land. 

deeper  furrows  are  now  generally  used  in  the  irrigation 
of  orchards  and  other  crops.  Fortier  and  others  have 
shown  that  the  deep  furrow  has  a  decided  advantage 
over  the  shallow  furrow.  (Figs.  51,  53-55.) 

The  furrow  method  is  in  many  ways  an  ideal  method 
of  irrigation.  It  enables  the  farmer  to  control  the  quantity 
of  water  added  to  a  soil.  It  makes  it  possible  to  spread  a 
small  quantity  of  water  over  a  relatively  large  area  of 
land.  It  prevents  the  washing  and  consequent  destruc- 


212 


IRRIGATION  PRACTICE 


tion  of  the  light  soils  characteristic  of  arid  regions.  It 
reduces  evaporation;  tends  to  prevent  over-irrigation, 
and,  because  of  the  ease  with  which  the  furrow  may  be 
covered,  soon  after  irrigation,  the  rise  of  alkali  is  delayed. 
There  is  little  disturbance  of  the  top  soil,  and  baking  is 


FIG.  53.  Standpipe  supplying  furrows  with  water. 

largely  eliminated.  The  system  once  laid  off  requires 
little  attention;  one  man  can  irrigate  a  large  number  of 
acres  in  one  day.  The  method  is  inexpensive. 

The  furrow  method  of  irrigation  also  has  some  dis- 
advantages. Large  heads  of  water  cannot  be  used  in  the 
small  furrows.  It  may  be  desirable,  especially  in  the 
spring,  to  apply  quickly  a  large  quantity  of  water  to  a 
given  field.  This  is  practically  impossible  with  the  fur- 
row method  of  irrigation.  It  is  difficult  to  admit  the 
same  quantity  of  water  to  each  of  the  many  furrows. 
Special  attention  must,  therefore,  be  given  to  establishing 
checks  in  the  supply  ditch  at  suitable  intervals,  to  force, 
as  nearly  as  may  be,  the  same  quantity  of  water  into  each 
furrow.  Tubes  or  lath  boxes,  connecting  the  furrows  with 
the  supply  ditch,  are  helpful  in  establishing  a  steady  flow 
in  each  furrow.  (Fig.  56.)  The  uniform  use  of  water 


METHOD  OF  IRRIGATION 


213 


throughout  the  length  of  the  furrow  is  very  difficult.  On 
sandy  soils,  especially,  the  upper  end  of  the  furrow 
absorbs  so  much  water  that  little  is  left  for  the  lower  end. 
In  fact,  when  the  furrow  is  long,  it  frequently  happens 
that  the  water  disappears  before  the  lower  end  is  reached. 
The  best  way  to  overcome  this  difficulty  is  probably  to 
shorten  the  furrows,  and  to  have  a  series  of  temporary 
supply  ditches  for  each  series  of  furrows. 

Finally,  the  soil  is  benefited  by  being  occasionally 
covered  with  water.  The  Utah  work  showed  that,  with 
a  given  quantity  of  water,  as  large  yields  were  invariably 
obtained  when  the  water  was  applied  by  flooding  as  by 
furrowing,  in  spite  of  the  greater  loss  by  evaporation 


FIG.  54.  Zigzag  furrows  to  insure  uniform  distribution  over  soil. 


214 


IRRIGATION  PRACTICE 


under  the  flooding  method.    It  may  be  well,  therefore,  to 
allow  the  water  to  overflow  occasionally  even  under  the 

furrow     method    of 

irrigation.  The  same 
effect  may  be  ob- 
tained 
placing 


in    part    by 
the    furrows 
differently  from  year 
to  year.     Meanwhile, 
the    furrow    method, 

FIG.  55.  Another  type  of  zigzag  furrows.  •,-, 

with  a  given  quantity 

of  water,  will  yield  as  heavily  as  will  the  flooding  method, 
and  may  yield  more.  , 

126.  Summary. — In  brief,  there  are,  in  practice,  only 
two  great  methods  of  irrigation:  (1)  flooding  by  field 
ditches,  and  (2)  furrowing.  The  field-ditch  method  is  in 
reality  a  furrowing  method,  in  which  the  water  overflows 
the  banks  of  the  fur- 
rows. On  certain  soils 
and  under  certain 
conditions  the  field- 
ditch  method  will  be 
found  most  service- 
able; on  others,  the 
furrowing  method. 
The  closed  field 
methods  are  likely  to  vanish  quite  rapidly  because  of 
the  large  expense  of  installation  and  the  want  of  elastic- 
ity in  the  system.  The  method  of  irrigation  by  furrows 
will  probably  triumph  as  the  great  method  of  applying 
water  to  soils  for  the  production  of  crops.  At  the  present 
time  the  field-ditch  and  the  furrowing  methods  are  in 
chief  use. 


Fia.  56.  Lath-box  for  distributing  water  to 
furrows  from  head  ditch. 


METHOD  OF  IRRIGATION  215 


REFERENCES 

FORTIER,  SAMUEL.  Methods  of  Applying  Water  to  Crops.  United 
States  Department  of  Agriculture,  Yearbook  for  1909,  p.  293. 

FORTIER,  SAMUEL,  and  BECKETT,  S.  H.  Evaporation  from  Irrigated 
Soils.  United  States  Department  of  Agriculture,  Office  of 
Experiment  Stations,  Bulletin  No.  248  (1912). 

LOUGHRIDGE,  R.  H.  Distribution  of  Water  in  the  Soil  in  Furrow 
Irrigation.  United  States  Department  of  Agriculture,  Office 
of  Experiment  Stations,  Bulletin  No.  203  (1908). 

MEAD,  ELWOOD,  et  al.  Preparing  Land  for  Irrigation  and  Methods 
of  Applying  Water.  United  States  Department  of  Agriculture, 
Office  of  Experiment  Stations,  Bulletin  No.  145  (1904). 

WICKSON,  E.  J.  Irrigation  Among  Fruit-Growers  on  the  Pacific 
Coast.  United  States  Department  of  Agriculture,  Office  of 
Experiment  Stations,  Bulletin  No.  108  (1902). 

WroTSOE,  J.  A.  Factors  Influencing  Evaporation  and  Transpira- 
tion. Utah  Experiment  Station,  Bulletin  No.  105  (1909). 

WIDTSOE,  J.  A.,  and  MERRILL,  L.  A.  Methods  for  Increasing  the 
Crop-Producing  Power  of  Irrigation  Water.  Utah  Experi- 
ment Station,  Bulletin  No.  116  (1912). 


CHAPTER  XI 
CROP  COMPOSITION 

CROPS  have  been  valued  almost  entirely  by  weight.  A 
bushel  of  wheat  has  been  a  bushel  of  wheat,  providing  it 
weighed  sixty  pounds.  Of  late  years  it  has  been  determined 
that  the  quality  may  be  as  important  as  the  quantity 
in  determining  the  value  of  a  crop  as  a  food  for  man  or 
beast.  The  time  is  undoubtedly  near  when  crops  will  be 
judged  in  the  markets  by  quality  as  well  as  by  quantity. 

Many  agricultural  industries  already  make  significant 
use  of  quality  valuation.  Sugar-beet  factories  purchase 
beets  at  a  given  price  a  ton,  but  the  price  is  conditioned 
on  the  sugar  content,  and  the  contracts  with  the  farmers 
always  specify  a  minimum  percentage  of  sugar.  Potatoes, 
when  made  into  starch  are  valued  on  the  basis  of  starch 
content.  Grains  are  graded  by  quality.  Fruits  are  classed 
according  to  color,  size  and  other  characteristics.  Many 
other  crops  are  likewise  valued  according  to  composition 
as  well  as  to  actual  weight. 

As  knowledge  concerning  food  and  its  relation  to  the 
animal  body  becomes  popularized,  there  will  be  an  increas- 
ing demand  for  foods  of  definite  composition  which  will 
affect  the  world  markets  until  a  scale  of  prices  based  on 
weight  and  composition  shall  be  established  for  each  crop. 
In  that  day,  the  irrigation  farmer  will  have  a  great  advan- 
tage, for  the  regular  variation  of  plant  composition  with 
the  quantity  of  water  applied  makes  it  possible  under 
the  controlled  water  supply  of  irrigation  to  regulate  in  a 

(216) 


CROP  COMPOSITION  217 

measure  the  quality  of  the  crops  produced.  Irrigation,  or 
the  artificial  application  of  water  to  crops,  requires  added 
labor.  It  is,  therefore,  only  upon  the  basis  of  certain 
and  larger  yields,  and  better  quality  of  the  crops  produced, 
that  irrigated  areas  may  compete  in  the  open  markets 
with  other  sections  of  the  world. 

The  relation  between  irrigation  and  crop  composi- 
tion has  been  studied  by  several  investigators.  In  general, 
it  has  been  shown  that  many  irrigated  crops  may  be 
made  to  possess  a  composition  superior  to  that  of  crops 
grown  under  the  natural  rainfall.  Yet,  it  must  be  admit- 
ted that  we  know  the  merest  outlines  of  the  subject. 
There  is  here  a  great  and  important  field  open  for  investi- 
gation by  those  who  are  interested  in  developing  a  science 
of  irrigation 

127.  Groups  of  plant  constituents. — Every  plant  con- 
tains five  great  groups  of  substances  and  each  has  a  defi- 
nite food  value  and  bears  important  relationships  to  the 
soil  on  which  the  plant  has  been  grown.    These  are:  (1) 
water,   (2)  ash  or  mineral  matter,   (3)  nitrogenous  sub- 
stances, (4)  fats,  and  (5)  carbohydrates. 

128.  Water. — During  the  life  of  the  plant,  large  quan- 
tities of  water  are  passed  rapidly  from  the  soil  into  the 
plant,  and  from  the  plant  leaves  into  the  air.   As  has  been 
shown,   hundreds  of  pounds  of  water  are  thus  passed 
through  the  plant  for  the  production  of  one  pound  of  dry 
matter.    That  the  vital  processes  of  the  plant  may  pro- 
ceed unhindered,  the  cells  of  the  green  plant  must  be  fully 
filled  with  water.   The  more  water  is  in  the  soil,  the  more 
completely  are  the  plant  cells  filled  with  water.    That  is, 
on  a  moist  soil,  under  conditions  of  abundant  irrigation, 
the  green  plant  probably  contains  a  larger  proportion  of 
water  than  on  dry  soils,  where  the  quantity  of  irrigation 


218  IRRIGATION  PRACTICE 

water  applied  is  small.  This  effect  is  felt  most  in  the 
stalks  of  plants.  In  the  leaves,  which  naturally  contain 
less  water  than  do  the  stalks,  the  effect  of  varying  quan- 
tities of  water  is  not  so  apparent;  but  the  water  content 
of  every  part  of  the  plant  is  somewhat  affected  by  the 
water  supply.  The  underground  parts  of  plants,  such  as 
potatoes  and  sugar  beets,  contain  usually  a  slightly 
larger  percentage  of  moisture,  when  grown  on  land 
abundantly  irrigated. 

Since  most  crops  are  not  sold  green,  this  effect  of  irri- 
gation has  little  commercial  value.  True,  in  the  case  of 
fruits,  tomatoes  and  similar  crops,  which  are  usually  dis- 
posed of  in  an  undried  condition,  the  increased  percent- 
age of  water  in  crops  grown  with  much  water  may  make 
considerable  difference  in  the  final  weight.  Potatoes  and 
sugar  beets,  when  irrigated  heavily  and  late,  may  weigh 
more  per  acre,  but  the  increased  yield  is  obtained  only  at 
the  sacrifice  of  quality.  In  most  cases  the  difference  is 
so  small  as  to  be  negligible. 

The  water  content  of  hay,  grain  and  other  crops  that 
are  sold  after  thorough  curing  or  ripening,  is  not  influenced 
by  the  irrigation  during  growth.  However,  hay,  cured 
under  the  dry  conditions  of  the  arid  region,  contains  less 
water  and  is  to  that  extent  more  valuable  than  hay  cured 
in  the  humid  regions.  Likewise,  the  water  content  of 
wheat  and  similar  crops  that  ripen  before  harvesting  is 
only  slightly  influenced  by  the  degree  of  irrigation;  but 
the  dry  conditions  of  the  arid  region  tend  to  yield  crops 
containing  less  water  than  when  grown  under  humid 
conditions.  In  short,  irrigated  crops  of  the  arid  region, 
that  are  dried  before  being  placed  on  the  market,  are  more 
valuable,  pound  for  pound,  than  those  grown  in  humid 
regions,  for  the  reason  that  under  humid  conditions  the 


CROP  COMPOSITION 


219 


drying-out  cannot  be  so  complete.  Stewart  has  shown 
that  this  difference  may  have  very  noticeable  financial 
results  when  large  shipments  of  grain  are  made  from  the 
arid  regions. 

129.  Ash. — The  ash,  or  incombustible  portion  of 
plants,  represents,  roughly,  the  food  taken  from  the  soil 
by  the  plant.  It  is,  therefore,  important  in  considering 
the  maintenance  of  soil  fertility.  The  effect  of  much  or 
little  soil  moisture  upon  the  quantity  of  ash  taken  up 
by  the  plant  has  been  investigated  by  many  students.  In 
general,  the  percentage  of  ash  in  the  dry  substance  be- 
comes larger  as  the  quantity  of  irrigation  water  or  the 
soil  moisture  increases.  The  following  table  shows  some 
typical  results  under  irrigated  conditions : 


Percentage 

of  ash  in  dr^ 

Y  matter  of 

irrigation 

Oat 
leaves 

Oat 
stalks 

Oat 
heads 

Sugar 
beets 

Potato 
tubers 

Large   

21.10 

8.68 

638 

6  15 

3  36 

Medium  .... 
Small 

19.57 
17  13 

7.72 
7  27 

6.03 
5  29 

6.02 
6  18 

3.89 
4  39 

As  the  supply  of  water  increases,  there  is  usually  a 
very  marked  increase  in  the  percentage  of  ash  in  the 
leaves,  a  smaller  increase  in  the  stalks,  and  a  yet  smaller 
increase  in  the  underground  parts  of  the  plant.  This 
relative  variation  among  the  plant  parts  seems  to  be  a 
general  rule,  although  observations  are  on  record  show- 
ing a  decrease  in  the  percentage  of  ash  hi  the  under- 
ground parts  as  the  irrigations  are  made  larger. 

Tollens  and  others  have  shown  that,  in  general,  this 
law  of  increase  is  true  for  each  ash  constituent  as  for  the 
total  ash.  Lime  is  taken  up  very  abundantly  by  the  plant 


220  IRRIGATION  PRACTICE 

as  the  supply  of -water  increases;  and  potassium,  phos- 
phorus, and  other  important  plant-foods  are  likewise 
taken  up  in  larger  proportion  to  the  dry  matter  as  the 
supply  of  water  is  increased. 

This  law,  that  the  percentage  of  ash  in  plants  increases 
as  the  irrigation  water  is  increased,  means,  apparently, 
that  more  plant-food  is  used  to  produce  a  unit  of  dry 
matter  as  more  water  is  used  in  irrigation.  This  is  one  of 
the  strongest  arguments  yet  found  against  the  excessive 
use  of  water.  The  farmer  who  uses  a  small  quantity  of 
water  in  crop-production  not  only  obtains  a  larger  amount 
of  dry  matter  for  each  unit  of  water  used,  but  also  uses  a 
smaller  quantity  of  plant-food  for  each  unit  of  dry  matter. 
The  waste  due  to  over-irrigation  is,  therefore,  at  least 
twofold :  it  diminishes  the  yield  of  dry  matter  to  the  unit 
of  water  used,  and  it  increases  the  soil-fertility  cost  per  unit 
of  dry  matter.  This  must  be  a  fundamental  considera- 
tion in  the  establishment  of  a  permanent  system  of  agri- 
culture under  irrigation. 

130.  Protein. — Protein  is  the  term  commonly  applied 
to  all  organic  plant  substances  containing  nitrogen.  These 
nitrogenous  plant  constituents  are  of  greatest  impor- 
tance in  the  maintenance  of  animal  life.  When  organized 
into  proteid  forms,  they  form  the  basis  of  blood,  muscles 
and  all  other  primary  tissues  of  the  animal  body.  In  fact, 
as  a  food  for  animals,  the  value  of  a  crop  may  be  well 
measured  by  its  percentage  of  nitrogenous  substances. 
The  compounds  containing  nitrogen  are  not,  however, 
all  of  equal  value.  Some  furnish  merely  body  heat,  while 
others  enter  into  the  fundamental  structures  of  the  body. 
In  the  investigations  of  the  effect  of  irrigation  on  plant 
composition,  attention  has  been  given  mainly  to  the  group 
of  substances  under  the  name  "protein,"  and  little  knowl- 


CROP  COMPOSITION 


221 


edge  exists  concerning  the  variations  of  the  individual 
compounds  occurring  under  this  general  head. 

The  percentage  of  protein  in  plants  is  very  sensitive  to 
irrigation.  The  more  water  used,  the  smaller  is  the  per- 
centage of  protein  in  the  resulting  plant.  This  is  almost 
invariably  true.  In  the  following  table  is  given  the  per- 
centage of  protein  in  several  crops,  when  small,  medium 
or  large  quantities  of  water  were  used  in  the  production 
of  the  crop. 

PERCENTAGE  OF  PROTEIN  IN  DRY  MATTER  WITH  VARYING  DEGREES 
OF  IRRIGATION 


Crop 

Degree  of  irrigation 

Small 

Medium 

Large 

Wheat  kernels.    Shallow  soil  
Wheat  kernels.    Deep  soil   

Per  cent 
26.72 
18.05 
8.88 
3.50 
19.74 
26.08 
9.83 
15.42 
12.24 
15.43 
15.08 
17.94 
1.67 
1.43 
2.87 
7.76 
8.36 
8.14 
6.52 
4.21 
4.34 
5.57 

Per  cent 
23.02 
16.45 
7.11 
3.17 
18.65 
23.32 

10.91 
13.81 
13.17 
17.44 

Per  cent 
15.26 
15.98 
5.86 
2.72 
17.81 
21.96 
5.16 
14.16 
9.49 
12.69 
12.05 
16.50 
0.94 
1.17 
1.26 
5.66 
4.33 
5.19 
6.42 
3.87 
2.42 
4.48 

Oat  leaves  .... 

Oat  stalks  

Pea  kernels 

Sugar  beets  (leaves) 

Potatoes  (tubers)      .    . 

Potatoes  (leaves)  

Corn  kernels  

Alfalfa.    Third  crop      

Apples,  Gano 

Apples,  Jonathan      . 

Pears,  Bartlett  ...... 

Blackberries  

Grapes    

Strawberries 

Peaches,  Elberta 

Plums,  Green  Gage  
Cherries,  Bing   

Every  crop  in  the  table,  even  apples,  pears  and  small 
fruits,  shows  a  diminishing  percentage  of  protein  with 
an  increasing  volume  of  irrigation  water.  The  law  is 


222  IRRIGATION  PRACTICE 

undoubtedly  of  very  wide  application.  In  the  above 
table,  the  percentage  of  protein  in  plant  parts  is  also  given. 
In  general,  the  percentage  of  protein  is  diminished  in 
every  part  of  the  plant  when  the  irrigation  is  increased. 
The  little  existing  knowledge  indicates  that  the  proteid 
parts  of  protein,  used  in  the  production  of  blood  and 
muscle,  are  affected  by  varying  irrigations,  even  more 
strongly  than  is  the  protein,  and  in  the  same  direction. 
Some  little  work  has  also  been  done  upon  protein  digesti- 
bility as  affected  by  irrigation;  and  it  seems  safe  to  assert 
that  when  crops  are  grown  with  increasing  quantities  of 
water  there  is  a  decreasing  percentage  of  digestible, 
nitrogenous  substances  in  the  plant.  It  is  clear,  there- 
fore, that  plants  and  plant  parts  are  more  valuable  as 
animal  foods,  pound  for  pound,  when  grown  with  little 
water. 

The  quantity  of  nitrogen  taken  up  by  a  crop  is  not, 
however,  largely  affected  by  irrigation.  Whether  the  crop 
has  received  much  or  little  irrigation  water  during  the 
period  of  growth,  the  total  quantity  of  protein  that  it 
contains  per  acre  is  approximately  the  same.  For  most 
crops  the  tendency  is  for  the  total  yield  of  protein  to 
increase  with  much  irrigation,  though  the  percentage 
decreases. 

The  compounds  of  nitrogen  from  which  protein  is 
made,  are  taken,  as  is  the  ash  previously  discussed,  by 
the  roots  from  the  soil.  It  would  be  expected,  therefore, 
that  the  protein  should  vary  as  does  the  ash  content. 
Instead,  the  variation  is  the  opposite.  Nitrogen  is  pres- 
ent in  the  soil  in  relatively  small  amounts,  and,  in  its 
soluble  and  available  forms,  in  even  smaller  amounts. 
Nitrification  and  similar  processes  which  convert  the 
organic  nitrogen  into  forms  available  to  plants  go  on  at 


CROP  COMPOSITION  223 

a  slow  rate.  In  the  spring  and  early  summer  when  the 
demand  of  the  young  plant  for  protoplasmic  material  is 
greatest,  the  relatively  small  quantities  of  available 
nitrogen  in  the  soil,  accumulated  since  the  last  harvest, 
are  eagerly  and  quickly  absorbed.  From  then  on,  the 
small  supply  of  nitrogen  is  that  made  available  by  nitrifi- 
cation and  similar  processes.  Moreover,  after  the  proto- 
plasmic materials  have  once  been  made,  it  is  doubtful  if 
the  plant's  demand  for  nitrogen  continues  unabated. 

The  protein  in  the  plant  is  thus  obtained  in  the  early 
stages  of  growth.  Carbon  assimilation,  however,  con- 
tinues until  the  period  of  ripening,  and  the  more  water 
used  the  more  dry  matter  produced.  In  any  case,  after 
the  first  periods  of  growth,  dry  matter  is  formed  more 
rapidly  than  protein.  Consequently,  the  percentage  of 
protein  in  the  dry  matter  decreases  as  the  plant  grows 
older  and  as  more  water  is  used.  This  seems  to  be  the 
simplest  explanation  of  the  important  law  that  the  larger 
the  irrigation,  the  smaller  the  percentage  of  protein  in  the 
dry  matter  produced  by  plants. 

Whatever  explanation  may  be  found  for  this  law,  the 
fact  remains  that  the  decreasing  percentage  of  protein 
with  increasing  irrigation  is  another  strong  argument  in 
favor  of  the  use  of  little  water  in  the  production  of  crops 
under  irrigation. 

131.  Fat. — The  quantity  of  fat  in  plants,  except  in 
the  few  crops  especially  grown  for  their  fat  content,  is 
so  small  as  to  be  of  little  consequence.  Little  is  known  of 
the  effect  of  irrigation  on  the  content  of  fat  in  plants. 
The  more  water  used  in  irrigation,  the  larger,  usually,  the 
percentage  of  fat  in  the  plant.  This,  however,  is  subject 
to  revision  as  more  knowledge  concerning  the  matter  is 
obtained. 


224  IRRIGATION  PRACTICE 

132.  Carbohydrates. — The  substances  included  in  this 
group  are  used  hi  the  animal  body  for  the  production  of 
heat  and  the  formation  of  fat.    The  carbohydrates  are 
very  important  foods;  but,  since  they  are  quite  abun- 
dant, they  are  of  less  value  than  the  protein.  The  elements 
constituting  the  carbohydrates  are  drawn  from  the  water 
of  the  soil  and  the  carbon  dioxide  of  the  air,  both  of  which 
are  more  easily  supplied  than  the  ash  or  the  nitrogen, 
the  essential  element  in  protein.    For  agricultural  pur- 
poses it  is  necessary  to  consider  under  the  head  of  carbo- 
hydrates the  sugars,  starches,  and  the  woody  substances 
or  crude  fiber.    It  has  been  well  established  that  the  per- 
centage of  total  carbohydrates  in  a  plant  increases  as  the 
quantity  of  irrigation  water  increases.    That  is,  the  per- 
centage of  the  sum  of  all  the  carbohydrates  varies  in  the 
opposite  direction  from  protein,  as  the  quantity  of  irriga- 
tion water  is  varied. 

133.  Sugars. — The  sugars  are  many.   The  best  known 
is  beet  or  cane  sugar.  As  a  general  though  not  an  invariable 
rule,  the  percentage  of  sugar  in  a  crop  decreases  as  irriga- 
tion water  increases.    In  the  following  table  are  presented 
a  number  of  data  secured  by  Jones  and  Palmer,  in  a  study 
of  fruits  grown  in  Idaho.   In  the  one  column  is  the  com- 
position of  irrigated,  in  the  other  of  non-irrigated  fruits. 
The  locality  in  which  these  fruits  grew  receives  a  rather 
large  rainfall,  and  the  conditions  are  not  those  prevailing 
under  true  arid  conditions.  •  The  non-irrigated  crops  may, 
therefore,  really  be  compared  to  those  that  have  received  a 
small  irrigation,  and  the  irrigated  crops  to  those  that  have 
received  a  heavy  irrigation: 


CROP  COMPOSITION 


225 


PERCENTAGE  OF  TOTAL  SUGAR  AND  ACIDS  IN  DRY  MATTER 


Total 

sugar 

Acids  (as 

HaS04) 

Crop 

Irrigated 

Non- 
irrigated 

Irrigated 

Non- 
irrigated 

Cherries,  Bing  

49.10 

53.08 

3.48 

2.55 

Peaches,  Crawford   .... 
Plums,  Green  Gage      .    .    . 
Prunes   Italian 

59.91 
48.20 
37.28 

65.12 
35.17 
48.31 

3.63 
4.05 
4.12 

3.90 
7.05 
3  63 

Apples   Gano    .        .... 

63.55 

61.70 

1.97 

1.50 

Apples,  Jonathan     .... 
Blackberries      

64.05 
43.72 

63.25 
23.85 

2.30 
3.22 

2.32 

5.28 

Dewberries    

37.37 

34.52 

3.05 

7.18 

Grapes,  Delaware    .... 
Loganberries 

45.41 
38.89 

43.26 
30.22 

2.79 
8.19 

3.16 
1347 

Strawberries      

42.69 

36.35 

5.88 

4  95 

Cherries,  peaches,  and  prunes  contained  most  sugar 
and  least  acids  when  receiving  small  irrigations.  That  is, 
these  fruits  became  more  sour  as  more  water  was  used, 
On  the  other  hand,  plums',  apples,  grapes,  loganberries 
and  strawberries  became  sweeter  as  the  irrigation  water 
was  increased.  Much  work  is  yet  to  be  done  before  we 
shall  know  the  full  truth  regarding  this  matter.  Mean- 
while, from  practical  experience  it  is  safe  to  predict  that 
it  will  be  found  that  the  moderate  irrigation  of  fruit 
orchards  will  produce  the  sweetest  fruit. 

Investigations  have  been  made,  also,  on  the  effect  of 
irrigation  on  the  percentage  of  sugar  hi  sugar  beets.  Up 
to  a  certain  low  limit  the  percentage  of  sugar  increases 
as  irrigation  increases.  When  excessively  large  quanti- 
ties of  water  are  used,  there  may  be  a  decided  increase  in 
sugar.  With  small  and  medium  applications  the  differ- 
ences in  the  percentages  of  sugar  are  relatively  small. 
This  is  shown  in  the  following  table,  which  contains 
average  results  of  many  years'  experimentation  by  the 
Utah  Station: 


226  IRRIGATION  PRACTICE 


Inches  of  irrigation 
water  applied 

Per  cent  sugar 
in  juice 

Per  cent  purity 
in  juice 

10 

15.33 

80.46 

20 

15.13 

81.09 

35 

15.41 

79.54 

When  the  water  used  was  increased  from  10  to  35 
inches,  there  was  increase  of  less  than  one-tenth  of  1  per 
cent  of  sugar  and  a  difference  of  only  about  1  per  cent 
in  the  purity  of  the  juice.  Moderate  irrigations  are 
undoubtedly  quite  as  satisfactory  as  larger  ones  in  pro- 
ducing beets  with  a  high  percentage  of  sugar.  Potatoes 
and  other  crops  yielding  much  sugar,  contain  the  highest 
percentages  of  sugar  when  medium  quantities  of  water 
are  used.  In  general,  sweeter  crops  are  produced  by 
moderate  than  by  either  very  small  or  very  large  irriga- 
tions. 

134.  Starch. — Starch,  one  of  the  important  foods  of 
man,  is   found   generally  in  plants.    In  potatoes,  sugar 
beets  and  similar  crops  it  is  a  chief  constituent.    In  the 
dry  matter  of  sugar  beets  the  percentage  of  starch  increases 
very  rapidly  with  the  increase  in  irrigation.  That  is,  where 
large  quantities  of  water  are  applied  to  sugar  beets,  much 
of  the  sugar  is  rapidly  converted  into  starch.    This  is 
another  argument  against  the  use  of  large  quantities  of 
water  in  irrigation.    In  the  dry  matter  of  potatoes,  grown 
largely  for  starch,  the  percentage  of  increase  hi  starch, 
due  to  increasing  irrigation,  is  much  slower.   In  general, 
the  starch  content  increases  as  irrigation  increases. 

135.  Woodiness. — The  woody  material  or  crude  fiber 
of  plants,  made  up  largely  of  cellulose,  is  of  little  value 
as  a  food.    It  is  influenced  very  strongly  by  irrigation 
water.   As  the  irrigation  water  applied  to  a  crop  increases 


CROP  COMPOSITION  227 

the  crude  fiber  remains  practically  constant  in  the  leaves, 
increases  rapidly  in  the  stalks,  and  increases  slowly  in  the 
underground  parts.  In  hay  crops  the  increase  is  not  great 
so  long  as  moderate  quantities  of  water  are  applied,  but 
when  excessive  quantities  are  applied,  the  crude  fiber  in 
all  crops  increases  very  rapidly.  Woody  crops  are  usually 
the  result  of  over-irrigation. 

136.  Color  and  flavor. — It  is  the  general  experience 
that  lightly  irrigated  crops  have  the  best  color.    Apples 
or  peaches,  grown  with  moderate  quantities  of  water, 
are  highly  colored,  while  those  receiving  large  quantities 
of  water  are  of  a  paler  color.    Under  conditions  otherwise 
the  same,  the  difference  is  not  great,  unless  an  excessive 
quantity  of  irrigation  water  be  applied.    The  flavor  of 
fruits  is  usually  better  when  medium  quantities  of  water 
arc  used.    In  some  crops,  as  wine  grapes,  this  is  of  great 
importance.   The  flavor  of  the  grape  is  transferred  to  the 
wine,  and  often  determines  the  value  of  the  beverage. 
When  the  irrigation  water  used  is  insufficient  to  produce 
a  commercial  crop,  it  often  happens  that  small  quantities 
of  splendidly  flavored  fruit  are  obtained.    In  practice, 
the  best  color  and  flavor  are  obtained  when  moderate 
quantities  of  water  are  used  hi  irrigation. 

137.  Flour. — The   composition   of  the   wheat   kernel 
is  strongly  affected  by  irrigation.   Much  water  produces  a 
soft  wheat;  little  water  a  hard  wheat.   High  protein  wheat 
is  obtained  with   small   irrigations;   low  protein  wheat 
with  large  irrigations.   This  difference  in  the  composition 
of  the  original  kernel  is  transferred  to  all  milling  products 
of   the   wheat — bran,   shorts   and   flour.     For   instance, 
in  flour  made  from  wheat  grown  with  much  water,  there 
was  12.63  per  cent  of  protein;  with  a  medium  amount  of 
water,  12.92  per  cent,  and  with  no  irrigation  water,  13.62 


228  IRRIGATION  PRACTICE 

per  cent.  Similar  variations  were  found  in  all  the  essen- 
tial characters  of  the  flour.  Unquestionably,  since  millers 
demand  hard  and  high  protein  wheat,  the  time  is  near 
when  grain  grown  with  much  irrigation  water  will  not  be 
considered  for  flour-production  on  the  markets  of  the 
world.  Irrigated  sections  that  still  produce  grain  for 
flour  should  govern  their  irrigation  practices  in  accord- 
ance with  the  needs  of  millers. 

138.  Cooking  value. — While  very  little  definite  infor- 
mation on  the  subject  exists,  it  is  fairly  certain  that  the 
cooking  value  of  fruits,   vegetables  and  other  crops  is 
affected  by  the  quantity  of  water  used  in  irrigation.    In 
one  reported  experiment,  it  seemed  that  potatoes  grown 
with  a  medium  quantity  of  water  were  whiter  and  mealier 
than  were  those  grown  with  more  water.    Similarly,  the 
flavor  of  vegetables  is  changed  by  the  quantity  of  water 
used  in  irrigation.    This  is  a  very  interesting  field  for 
investigation,  especially  by  those  interested  in  the  food 
branch  of  home  economics. 

139.  Effect  of  cultural  treatment. — It  is  evident  from 
this  discussion  that  the  more  moisture  there  is  in  the  soil 
the   higher   the   percentage   of   ash,    carbohydrates   and 
crude  fiber,  and  the  lower  the  percentage  of  protein.   Any 
cultural   treatment   which   results   in   maintaining  more 
moisture  in  the  soil  during  the  growing  period  would, 
therefore,  have  the  same  effect  as  if  more  water  had  been 
added  to  the  soil.    The  thorough  cultivation  of  the  soil 
to  prevent  evaporation  conserves  the  moisture  in  the  soil. 
In  the  Utah  work,  it  was  found  that  the  percentage  of 
protein  was  lower  in  crops  grown  on  well-cultivated  soils 
than  in  those  grown  on  soils  receiving  little  or  no  cultiva- 
tion.   Under  the  furrow  method  of  irrigation,  the  per- 
centage of  protein  in  the  resulting  crop  was  somewhat 


CROP  COMPOSITION 


229 


higher  than  under  the  flooding  method.  However,  the 
composition  of  the  crop  showed  the  greatest  sensitive- 
ness to  cultural  methods  in  the  matter  of  the  time  of 
applying  irrigation  water.  Some  of  the  results  obtained 
are  shown  in  the  following  table: 


Inches  of 
irrigation  water 
applied 

Time  of  application 

Per  cent  protein 
in  dry  matter 
of  grain 

3.5 
3.5 

At  usual  time. 
Later  at  time  of  "filling  out." 

21.75 

18.84 

7.5 
7.5 
7.5 

Two  irrigations  (5.0;  2.5) 
Two  irrigations  (2.5;  5.0) 
Two  irrigations  (3.75;  3.75) 

17.81 
16.65 
16.21 

10.0 
10.0 
10.0 

Two  irrigations  (7.5;  2.5) 
Two  irrigations  (2.5;  7.5) 
Two  irrigations  (5.0;  5.0) 

17.17 
16.40 
16.01 

Clearly,  the  response  of  the  composition  of  the  crop 
to  the  time  of  application  is  greatest  when  the  total 
quantity  of  water  used  is  small.  It  seems  to  be  the  invari- 
able rule  that  when  the  greater  part  of  the  water  is  applied 
early  in  the  season,  the  percentage  of  protein  is  highest. 
On  the  other  hand,  when  the  distribution  is  such  that 
the  percentage  of  moisture  remains  constant  throughout 
the  growing  season,  the  percentage  of  protein  falls.  When 
water  is  so  applied  that  a  high  moisture  period  is  followed 
by  a  low  moisture  period,  the  protein  percentage  increases. 
A  more  complete  examination  of  this  subject  might  go 
far  in  determining  the  time  at  which  water  should  be 
applied.  It  offers  an  alluring  field  of  experimentation 
for  those  engaged  hi  irrigation  study. 

The  time  at  which  grain  is  planted  also  helps  to 
determine  the  composition  of  grain.  When  planted  in 


230  IRRIGATION  PRACTICE 

the  fall,  it  grows  partly  in  the  fall,  freezes  down,  and  then 
grows  again  early  in  the  spring,  before  the  spring  wheat 
is  planted.  Fall  wheat  has,  therefore,  a  longer  growing 
period  than  has  spring  wheat,  and  there  is  more  water 
available  for  fall  than  for  spring  wheat.  Consequently 
winter  wheat  contains  a  smaller  percentage  of  protein 
than  does  spring  wheat.  In  an  experiment  continued 
eight  years,  it  was  found  that  fall-sown  wheat  contained 
15.75  per  cent  of  protein,  whereas  spring-sown  wheat 
contained  16.85  per  cent  of  protein.  Similar  differences 
have  invariably  been  found  when  contrasting  spring- 
grown  and  fall-grown  grain. 

REFERENCES 

JONES,  J.  S.,  and  COLVER,  C.  W.  The  Composition  of  Irrigated  and 
Non-Irrigated  Fruits.  Idaho  Experiment  Station,  Bulletin 
No.  75  (1912). 

LE  CLERC,  J.  A.  A  Comparison  of  Irrigated  and  Non-Irrigated 
Wheat.  United  States  Department  of  Agriculture,  Yearbook 
for  1906,  p.  199. 

LEWIS,  C.  J.,  KRATJS,  E.  J.,  and  REES,  R.  W.  Orchard  Irrigation 
Studies  in  the  Rogue  River  Valley.  Oregon  Experiment  Sta- 
tion, Bulletin  No.  113  (1912). 

STEWART,  ROBERT  and  HIRST,  C.  T.  Comparative  Value  of  Irriga- 
tion and  Dry-Farming  Wheat  for  Flour-Production.  Journal 
of  Industrial  and  Engineering  Chemistry,  Vol.  IV,  No.  4,  April, 
1912. 

TOLLENS,  B.  The  Ash  Constitutents  of  Plants.  Experiment  Station 
Record,  Vol.  XIII,  Nos.  3  and  4. 

WIDTSOE,  J.  A.,  and  STEWART,  ROBERT.  The  Chemical  Composi- 
tion of  Crops  as  Affected  by  Different  Quantities  of  Irrigation 
Water.  Utah  Experiment  Station,  BuUetin  No.  120  (1912). 

WIDTSOE,  J.  A.,  and  STEWART,  ROBERT.  The  Effect  of  Irrigation  on 
the  Growth  and  Composition  of  Plants  at  Different  Periods  of 
Development.  Utah  Experiment  Station,  Bulletin  No.  119 
(1912). 


CHAPTER  XII 
THE  USE  OF  THE  RAINFALL 

RAIN  falls  upon  the  whole  surface  of  the  earth  Where 
there  is  much  rain,  the  country  is  called  humid;  where 
there  is  little  rain,  the  country  is  called  arid.  Humidity 
and  aridity  are  conditions  that  depend,  primarily,  upon 
the  water  that  falls  from  the  heavens  as  rain  or  snow, 
although  where  water-dissipating  factors,  such  as  winds 
and  shallow  soils,  are  small,  a  low  rainfall  may  be  more 
effective  than  a  high  rainfall  where  these  factors  are  large. 
Growing  plants  require  large  quantities  of  water.  Some 
of  this  necessary  water  evaporates  directly  from  the  soil; 
another  part  evaporates  from  the  leaves  of  the  plant; 
some  water  may  be  lost,  also,  by  seepage  through  the 
soil.  Unless  there  is  enough  water  in  the  soil,  it  is  impos- 
sible for  plants  to  thrive  and  to  yield  sufficient  returns 
to  the  farmer.  Irrigation  is  the  art  whereby  the  deficiency 
in  the  natural  rainfall,  whether  large  or  small,  is  supplied 
by  water,  artificially  added,  so  that  regular,  abundant 
crops  may  be  obtained. 

140.  Irrigation  supplementary  to  rainfall. — Such  a 
definition  of  irrigation  makes  it  evident  that  the  quantity 
of  water  to  be  used  hi  irrigation  depends  on  the  degree  of 
the  natural  precipitation.  The  higher  the  annual  rain- 
fall that  may  be  retained  hi  the  soil  for  crop  use,  the 
smaller  the  quantity  of  water  required  in  irrigation.  The 
lower  the  annual  rainfall  that  may  be  so  retained,  the 
higher  the  irrigation  requirement.  This  is  a  somewhat  new 

(231) 


232  IRRIGATION  PRACTICE 

thought  in  irrigation  practice.  Modern  irrigation  was 
founded  in  a  very  arid  country,  with  almost  rainless 
summers,  at  a  time  when  there  was  no  science  of  agricul- 
ture, and  by  men  who  had  had  no  previous  irrigation 
experience.  The  practice  of  irrigation  was,  therefore, 
founded  on  the  assumption  that  irrigation  was  a  primary 
art,  practically  independent  of  the  natural  precipitation. 
As  practical  irrigation  experience  was  gathered  it  became 
clear  that  any  rainfall,  even  a  small  one,  if  conserved  in 
the  soil,  has  crop-producing  power,  and  that  irrigation 
is  always  a  supplementary  art.  Irrigation  is  and  always 
should  be  supplementary  to  the  rainfall.  Consequently, 
the  first  big  irrigation  problem  is  to  conserve  the  rain- 
fall in  the  soil  for  crop  use,  so  that  the  available  irriga- 
tion water  may  be  made  to  cover  as  much  ground  as 
possible.  The  beginning  of  irrigation  wisdom  is  the  con- 
servation of  the  natural  precipitation  for  the  use  of 
crops. 

141.  Crop-producing  power  of  rainfall. — The  theoreti- 
cal productive  power  of  the  natural  precipitation  shows 
that  even  a  low  annual  rainfall,  properly  conserved,  may 
produce  fair  crops  without  irrigation.  It  has  been  shown 
previously  that  to  produce  one  pound  of  dry  matter  on 
a  fertile  soil  under  arid  conditions,  more  than  750  pounds 
of  water  are  seldom  required.  If  750  pounds  of  water 
are  required  to  produce  one  pound  of  dry  matter,  one 
bushel  of  wheat  will  require  for  its  production  90,000 
pounds,  or  forty-five  tons,  of  water.  On  this  basis,  each 
acre-inch  of  water — weighing  about  113  tons — should  pro- 
duce about  two  and  one-half  bushels  of  wheat.  An  annual 
precipitation  of  10  inches,  if  fully  conserved,  should  then 
produce  twenty-five  bushels  of  wheat  per  acre,  which  is  a 
high  average  crop. 


USE  OF  THE  RAINFALL  233 

142.  Results  of  dry-farming. — This  theoretical  demon- 
stration has  been  well  borne  out  by  the  results  of  the 
modern  art  of  dry-farming.    Dry-farming,  as  a  system  of 
agriculture,  attempts  to  produce  profitable  crops  without 
irrigation   on   soils   that   receive  an  annual   rainfall  of 
between  10  and  20  inches.   Where  there  are  high  winds  or 
other  water-dissipating  factors,  a  rainfall  of  from  20  to  30 
niches  a  year  also  requires  dry-farming  methods.    The 
two-thirds  of  the  area  of  the  earth's  surface  receiving 
annually  less  than  20  inches  of  rain,  are  the  so-called  arid 
and  semi-arid  regions  of  the  earth  on  which  irrigation 
has  been  held,  until  lately,  to  be  a  necessity  for  success- 
ful crop-production.    Yet,  successful  dry-farming,  during 
the  last  few  years,  has  been  practised  on  great  areas  that 
receive  between  10  and  20  inches  of  rainfall  annually. 
This  confirms  the  accuracy  of  the  theoretical  deduction 
of  the  crop-producing  power  of  the  rainfall. 

143.  Crop   value    of   rainfall   in    irrigation. — Experi- 
ments have  also  been  performed  to  discover  what  propor- 
tion of  a  crop  grown  under  irrigation  may  properly  be 
credited  to  the  natural  precipitation.    In  the  Utah  work, 
the  same  crop  was  planted  on  two  neighboring  plots. 
One  was  irrigated;  the  other  dry-farmed.     Both  plots 
yielded  crops,  and  it  was  assumed  that  the  yield  on  the 
plot  receiving  no  irrigation  was  the  same  as  the  part  of 
the  yield  under  irrigation,  due  to  the  natural  precipitation. 
Some  of  the  results  thus  obtained  are  given  in  the  follow- 
ing table.    In  reading  the  table,  it  should  be  remembered 
that  the  average  precipitation  under  which  the  work  was 
done  was  in  the  neighborhood  of  15  inches  a  year.   The 
soils  were  deep  and  of  splendid  water-holding  power,  and 
had  been  carefully  tilled  according  to  the  best  dry-farm 
methods,  so  as  to  conserve  the  natural  precipitation. 


234  IRRIGATION  PRACTICE 

PERCENT  OF  A  CROP  RAISED  WITH  ABOUT  7%  INCHES  OP  IRRI- 
GATION, DUE  TO  THE  NATURAL  PRECIPITATION 

Per  cent 

Wheat  (grain) 83.99 

Wheat  (straw) 86.42 

Oats  (grain) 85.67 

Oats  (straw) 98.19 

Corn  (grain) 81.14 

Corn  (stover) 83.03 

Alfalfa  (all  crops) 77.18 

Potatoes 66.89 

The  results  show  that  between  80  and  90  per  cent 
of  the  yield  of  grain  of  wheat,  oats  and  corn,  grown  with 
about  iy%  inches  of  irrigation  water,  was  really  produced 
by  the  natural  precipitation.  Even  larger  proportions 
of  straw  and  stover  were  so  produced.  With  the  same 
degree  of  irrigation,  77  per  cent  of  a  crop  of  alfalfa,  and 
67  per  cent  of  a  crop  of  potatoes,  were  produced  by  the 
natural  precipitation. 

Bark  and  Welch  carried  on  similar  experiments  on  the 
Gooding  Experiment  Station,  Idaho,  with  Blue  Stem, 
Sonora  and  Little  Club  wheats.  As  an  average  of  three 
years  of  work  with  these  wheats  it  was  found  that  of  a 
crop  raised  with  about  6  inches  of  irrigation  water,  about 
75  per  cent  of  the  yield  should  be  credited  to  the  natural 
precipitation.  This  confirms  the  Utah  work.  True,  on 
different  soils,  the  same  precipitation  would  produce  dif- 
ferent results,  and  these  figures  are  probably  maximum 
because  of  the  excellent  treatment  given  the  soil  and 
crops.  However,  a  considerable  proportion,  usually  from 
40  to  70  per  cent,  roughly  one-half,  of  the  crop  obtained 
under  irrigation  may  be  safely  credited  to  the  natural 
precipitation,  wherever  the  rainfall  is  over  12  inches 
annually  and  proper  methods  of  cultivation  are  practised. 
On  the  other  hand,  when  the  rainfall  is  not  conserved,  the 


USE  OF  THE  RAINFALL  235 

yields  under  irrigation  are  greatly  reduced.  As  the  rain- 
fall is  more  carefully  conserved,  the  area  that  may  be 
served  by  the  available  irrigation  water  will  be  greatly 
increased.  (Fig.  57.) 


Wheaf  Oofs  Corn  Lucern  Potatoes 

FIG.  57.  Yield  of  crops  due  to  rainfall.   Shaded  areas,  yields  with  irrigation;  black 
areas,  yields  without  irrigation. 

144.  Conserving  the  rainfall. — The  high  crop-produ- 
cing value  of  the  rainfall  in  irrigation  practice  makes  it 
important  to  understand  the  best  methods  whereby  the 
natural  precipitation  may  be  conserved.     (1)   The  top 
soil  must  be  kept  in  a  loose  condition,  so  that  the  water 
may  enter  the  soil  easily  and  completely  as  it  falls  from 
the  heavens.    (2)  The  soil  must  be  so  treated  by  thorough 
cultivation  that  the  water  which  enters  the  soil  will  be 
kept  there  until  needed  by  the  plant.   These  are  the  two 
chief  considerations  of  the  irrigation  farmer  who  desires  to 
get  the  greatest  possible  returns  from  the  rainfall. 

145.  Distribution   of   rainfall. — The   methods   to    be 


236  IRRIGATION  PRACTICE 

employed  in  water  conservation  vary  with  the  seasonal 
distribution  of  the  rainfall.  The  rainfall  varies  not  only 
from  place  to  place,  but  varies  also  in  its  seasonal  distribu- 
tion. Thus,  on  the  Pacific  seaboard,  west  of  the  Sierra 
Nevadas  and  the  Cascades,  the  wet  season  extends  from 
October  to  March,  with  a  practically  rainless  summer. 
This  is  the  Pacific  type  of  distribution.  Under  the  sub- 
Pacific  type,  which  extends  over  eastern  Washington, 
Nevada  and  Utah,  the  maximum  rainfall  is  shifted  toward 
the  early  spring,  but  the  summers  are  still  quite  rainless. 
Under  the  Arizona  type,  fully  developed  in  Arizona  and 
New  Mexico,  about  35  per  cent  of  all  the  rain  falls  in  July 
and  August,  and  May  and  June  are  generally  the  rainless 
months.  Under  the  Rocky  Mountain  foothills  type, 
most  rain  falls  from  April  to  June.  Finally,  under  the 
Plains  type,  embracing  the  larger  part  of  the  Dakotas, 
Nebraska,  Oklahoma  and  Texas,  the  heaviest  rains  come 
during  May  to  July,  when  crops  are  growing.  Moving 
eastward  from  the  Pacific  Coast  to  the  Great  Plains,  the 
major  rains  are  shifted  from  midwinter  to  midsummer. 
Moreover,  in  many  places  show  lies  long  on  the  ground 
in  the  winter,  while  in  other  places  there  is  no  snowfall. 
The  methods  of  conserving  the  rainfall  in  the  soil  must  be 
varied  somewhat  with  regard  to  the  prevailing  type  of 
precipitation.  Whether  rains  come  in  winter  or  summer 
they  must  be  stored  in  the  soil  for  some  time.  Especially 
where  the  rains  come  in  the  winter,  they  must  be  held  in 
the  soil  until  the  growing  season  arrives. 

146.  Storing  water  in  the  soil. — Well-plowed  soil  is  in 
a  good  condition  to  store  water  from  the  rains  and  snows. 
In  the  western  United  States,  where  the  summers  and 
falls  are  somewhat  rainless,  and  the  chief  precipitation 
comes  in  winter  or  early  spring,  fall  plowing  is  commonly 


USE  OF  THE  RAINFALL  237 

resorted  to  for  the  purpose  of  enabling  the  rains  to  enter 
the  soil.  Fall  plowing  is  practised  as  early  as  convenient, 
and  the  soil  is  frequently  left  in  the  rough  throughout 
the  winter.  The  fall,  whiter  and  spring  rains  are  quickly 
absorbed  by  such  land  and  stored  to  considerable  depths, 
as  already  explained  in  Chapter  III.  Where  the  chief 
precipitation  comes  in  late  spring  and  summer,  it  is 
sufficient  to  plow  in  early  spring  and  to  keep  the  soil  loose 
during  the  time  of  precipitation  by  tilling  after  each  rain. 

147.  Cultivation. — The  purpose,  effect  and  method  of 
cultivation  have  been  discussed  hi  Chapter  IV.    It  is  the 
best  known  method  for  retaining  the  natural  precipita- 
tion in  the  soil.    It  is  just  as  important  that  the  soil  be 
carefully  cultivated  after  a  rain  as  after  an  irrigation.    In 
the  spring  the  land  should  be  properly  harrowed  and  culti- 
vated, so  that  the  moisture  gathered  during  the  winter 
may  not  evaporate. 

148.  Proportion  of  rainfall  conserved. — In  the  inter- 
mountain  country,  where  the  precipitation  comes  in  winter 
or  early  spring,  it  has  been  found  that,  by  fall  plowing 
and  spring  cultivation,  from  60  to  90  per  cent  of  the  pre- 
cipitation between  harvest  and  spring  is  found  stored  in 
the  soil  in  the  spring.    In  the  region  where  the  rainfall 
comes  largely  in  spring  and  summer  it  has  been  found  that 
it  is  possible  to  store  in  the  soil  during  the  summer  sea- 
son from  40  to  60  per  cent  of  all  the  moisture  that  falls 
at  that  time.   Water  so  stored  in  the  soil  is  of  great  value 
in    producing    crops;    especially   valuable    is   the    water 
stored  in  the  soil  during  winter,  for  it  has  been  hi  very 
intimate  contact  with  the  soil  particles  and  is  heavily 
charged  with  plant-foods. 

149.  Relation  of  irrigation-  and  dry-farming. — There 
is   no   opposition    between   dry-farming   and   irrigation- 


238  IRRIGATION  PRACTICE 

farming.  They  are  twin  sisters.  Upon  them  rests  the 
responsibility  of  reclaiming  the  two-thirds  of  the  earth 
which  receive  an  annual  rainfall  of  less  than  20  inches. 
Newell  estimates  that  under  a  perfected  system  of  water 
storage,  it  is  probable  that  not  more  than  one-tenth  of 
this  vast  arid  region  will  be  reclaimed  by  irrigation.  The 
remaining  nine-tenths  must  be  reclaimed,  if  at  all,  by  the 
methods  of  dry-farming.  On  the  irrigated  lands  will  be  the 
great  cities  and  the  bulk  of  the  population,  but  surround- 
ing them  will  be  the  great  dry-farm  empires,  the  products 
of  which  will  help  support  the  people  on  the  irrigated 
tracts.  Since,  in  any  country,  the  supply  of  irrigation 
water  is  adequate  to  cover  only  a  small  fraction  of  the 
arid  lands,  it  is  important  to  learn  every  method  whereby 
irrigation  water  may  be  made  to  render  a  high  duty  and 
to  cover  more  land.  The  most  promising  method  for 
accomplishing  this  result  is  the  introduction  into  irriga- 
tion practices  of  methods  whereby  the  natural  precipita- 
tion may  be  conserved  in  the  soil.  That  is,  thorough  and 
deep  plowing  in  the  fall,  and  frequent  and  deep  cultiva- 
tion, should  be  made  part  and  parcel  of  irrigation  practices. 
When,  in  connection  with  this  thorough  tillage,  irrigation 
water  is  applied  in  smaller  quantities,  so  that  larger  returns 
may  be  obtained  for  each  unit  of  water,  it  is  not  unlikely 
that  the  irrigated  area  may  be  increased  three-  or  four- 
fold. From  the  beginning,  therefore,  the  irrigation  farmer 
should  familiarize  himself  with  the  methods  of  dry-farming 
and  apply  them  so  far  as  may  be  possible  in  the  develop- 
ment of  a  high  duty  of  the  available  irrigation  water. 

150.  Dry-farm  homesteads. — The  dry-farming  areas 
are  often  at  considerable  distances  from  large  water  sup- 
plies, although  small  springs  or  streams  or  subterranean 
waters  are  usually  within  reach.  In  some  cases  water 


USE  OF  THE  RAINFALL  239 

must  be  hauled  many  miles  to  the  dry-farms.  The  dry- 
farmer  can  do  his  work  most  effectively  if  he  can  build 
his  homestead  on  the  dry-farm  and  live  there  with  his 
family.  To  do  this  he  needs  to  have  a  small  irrigated 
garden  around  his  home,  with  some  trees  for  shade  and 
fruit.  A  clear  understanding  of  the  possibilities  of  irriga- 
tion water,  combined  with  dry-farming  methods,  will  make 
it  possible  to  establish  on  the  great  majority  of  the  dry- 
farms  throughout  the  country  small  homesteads,  where 
grass,  and  flowers  and  trees  may  be  enjoyed.  If,  then, 
dry-farming  methods  are  of  value  in  extending  the  irri- 
gated area,  the  possibilities  of  small  water  supplies  in  irriga- 
tion will  do  much  to  make  dry-farming  more  attractive 
to  those  who  practise  it. 

Dry-farming  and  irrigation  will  go  hand  in  hand  in 
redeeming  the  waste  places  of  the  earth.  Both  depend 
primarily  upon  the  natural  precipitation. 

REFERENCES 

CAMPBELL,  H.  W.    Soil  Culture  Manual.    Soil  Culture  Company. 

DRY-FARMING  CONGRESS,  Reports  of. 

FORTIER,  SAMUEL.  The  Use  of  Small  Water  Supplies  for  Irriga- 
tion. United  States  Department  of  Agriculture,  Yearbook  for 
1907,  p.  409. 

HILGARD,  E.  W.,  and  LOUGHRIDGE,  R.  H.  Endurance  of  Drought  in 
Soils  of  the  Arid  Region.  California  Experiment  Station,  Bulle- 
tin No.  121;  also  (fuller),  Report  for  1897-8,  p.  40  (1900). 

MACDONALD,  WM.   Dry-Farming.   Century  Company  (1910). 

MEAD,  ELWOOD.  The  Relation  between  Irrigation  and  Dry-Farm- 
ing. United  States  Department  of  Agriculture,  Yearbook  for 
1905,  p.  423. 

MERRILL,  L.  A.  Seven  Years'  Experiments  in  Dry-Farming.  Utah 
Experiment  Station,  Bulletin  No.  112  (1911). 

SHAW,  THOMAS.   Dry  Land  Farming  (1912). 

WIDTSOE,  J.  A.   Dry-Farming.   The  Macmillan  Company  (1911). 


CHAPTER  XIII 
IRRIGATION  OF  CEREALS 

WHEN  land  is  brought  under  irrigation,  the  small 
grains  form  the  first  of  the  staple  crops.  This  follows  from 
the  nature  of  the  cereals.  They  furnish  breadstuffs  to 
man,  and  their  by-products  are  excellent  concentrated 
foods  for  farm  animals.  A  ready  market  always  awaits 
the  small  grains,  and  they  bring,  therefore,  sure  and  quick 
returns  to  the  farmer  who  is  just  beginning  the  conquest 
of  an  irrigated  farm.  The  small  grains  mature  at  the  time 
of  large  water  supply,  and  for  that  reason,  need  less  atten- 
tion during  the  drier  period  of  the  growing  season.  Land 
is  easily  prepared  for  small  grains  and  the  cultural  opera- 
tions are  simple.  After  more  profitable  crops  have  been 
established  under  the  irrigation  system,  the  small  grains 
fit  well  into  the  rotations  necessary  for  the  maintenance 
of  soil  fertility.  Finally,  small  grains  may  be  grown  with 
limited  capital,  which  is  all-important  to  the  average  new 
settler. 

In  the  beginning  of  irrigation  in  the  United  States, 
the  small  grains  formed  the  bulk  of  the  crops  that  were 
raised.  Extensive  grain-growing  under  irrigation  is, 
however,  gradually  ceasing,  because  special  crops,  such 
as  sugar  beets  and  fruits,  yield  larger  acre  returns  than 
the  grains,  and,  moreover,  because  it  has  been  shown  that 
the  small  grains  are  particularly  well  adapted  for  growth 
under  dry-farming  methods  on  the  non-irrigated  lands. 
Then,  the  increasing  demand  by  millers  for  hard  wheats 

(240) 


IRRIGATION  OF  CEREALS  241 

will  gradually  diminish  the  market  value  of  the  softer 
wheats  produced  by  irrigation. 

Undoubtedly,  small  grains,  especially  wheat,  as  a 
major  crop,  will  gradually  be  driven  from  the  irrigated 
to  the  non-irrigated  lands,  although  they  will  always 
be  important  crops,  since  they  fit  well  into  rotations. 
Wherever  an  irrigation  enterprise  is  begun,  it  will  be 
found  profitable  to  grow,  for  some  years,  extensive  crops 
of  the  small  grains. 

151.  Spring  vs.  fall  wheat. — Wheat  may  be  considered 
as  a  type  of  the  small  grains.    Formerly,  under  irrigation 
practice,  spring  grains  were  sown  almost  entirely.    With 
the  advance  of  dry-farming,  which  is  characterized  by  fall 
sowing,  irrigated  grain  is  often  planted  in  the  fall.    The 
advantage  of  fall  planting  is  that  grain  so  sown  makes 
better  use  of  the  fall  and  winter  precipitation,  gets  an 
early  start  in  the  spring,  and  matures  earlier.    Moreover, 
less  water  is  required  to  bring  the  fall  grain  to  maturity 
and  to  a  high  yield.    In  harmony  with  the  spirit  of  econo- 
mizing irrigation  water,  the  sowing  of  fall  grain  should  be 
made  a  general  practice  in  irrigated  sections. 

152.  Quantity   of  wheat  to   sow. — The   quantity  of 
seed  to  sow  must  be  varied  with  the  quantity  of  irriga- 
tion water  available  throughout  the  season.    Under  dry- 
farming,  on  lands  that  receive  an  annual  precipitation  of 
12  to  15  inches,  twenty-five  to  thirty  pounds  of  wheat  are 
used  to  the  acre.    Under  irrigation,  with  the  same  annual 
rainfall,  one  to  three  bushels  of  seed  or  more  are  often 
used.  It  is  not  wise  to  use  too  much  seed,  for  the  numerous 
plants  that  result  demand  a  large  supply  of  water,  if  they 
are  to  be  brought  to  maturity;  and,  if  by  chance  the  water 
supply  should  be  cut  off  or  diminished,  the  excessive  num- 
ber of  plants  would  speedily  exhaust  the  soil  moisture 


242  IRRIGATION  PRACTICE 

and  become  seriously  injured.  A  common  experience  on 
dry-farms,  where  too  much  seed  has  been  used,  is  to  find  a 
splendid  stand  of  young  grain  in  the  spring,  and  failure 
at  harvest  time.  Under  irrigation,  as  under  dry-farming, 
the  number  of  plants  must  be  proportional  to  the  proba- 
ble water  supply.  If  the  number  of  plants  is  in  excess 
of  the  probable  water  supply,  the  yield  will  be  unsatis- 
factory. It  is  always  better  to  sow  limited  quantities 
of  seed,  for  by  stooling  there  is  an  automatic  adaptation 
of  the  wheat  plant  to  the  water  in  the  soil.  Experiment 
has  shown  that  where  little  seed  has  been  sown,  and  the 
water  has  been  sufficient,  the  harvest  is  as  great  as  if 
more  seed  has  been  sown.  No  material  change  in  the 
acre-yield  has  occurred  even  when  the  seed  sown  to  the 
acre  varied  from  four  to  twelve  pecks.  One  bushel  or  less 
is  probably  as  satisfactory  as  larger  quantities,  except  on 
very  rich  soils  with  an  abundance  of  water. 

153.  Method  of  sowing  wheat. — Wheat  and  the  other 
small  grains  should  always  be  planted  in  rows  by  some 
one  of  the  many  press  drills.  This  enables  the  farmer  to 
control  the  quantity  of  seed  used,  and  the  depth  and 
regularity  of  planting.  Under  irrigation,  the  yield  is 
influenced  by  the  distance  between  the  drill  rows.  Experi- 
ments on  this  subject  indicate  that  the  yield  is  increased 
when  the  same  quantity  of  seed  to  the  acre  is  planted  in 
rows  twice  as  far  apart.  This  may  be  due  to  the  greater 
chance,  under  such  conditions,  of  a  large  lateral  develop- 
ment of  the  roots. 

The  direction  of  the  drill  rows  may  be  of  considerable 
importance.  On  comparatively  level  land,  the  drill  rows 
may  help  guide  the  irrigation  water  from  place  to  place. 
On  rolling  land  and  steep  hillsides  the  drill  rows  may  be 
run  with  the  contour  lines,  i.  e.,  across  the  inclination. 


IRRIGATION  OF  CEREALS  243 

By  this  method,  the  rows  become  checks  to  the  descend- 
ing water,  and  washing  or  unnecessarily  rapid  flooding 
of  the  land  is  prevented. 

154.  Cultivation  of  wheat. — As  explained  in  Chapter 
IV,  cultivation,  properly  performed,  may  largely  take  the 
place  of  irrigation.    On  clayey  soils  there  is  a  tendency 
for  a  crust  to  form  after  each  irrigation,  which  should  be 
broken  to  prevent  serious  injury  to  the  plants.  The  present 
system  of  planting  grains  hi  rows  very  near  each  other 
makes  it  difficult  and  probably  unprofitable  to  give  such 
crops    inter-row    culture.     However,    wheat    fields    may 
safely  be  cultivated  while  the  plants  are  young — from  8 
to  12  inches  high — by  harrowing  with  an  ordinary  spike- 
tooth  harrow  with  the  teeth  set  backward,  so  that  few 
plants  will  be  torn  out.    The  corrugated  roller  is  some- 
times used  to  break  the  crust,  but  the  harrow  is  probably 
better,  since  it  does  not  compress  the  soil.    As  the  grain 
becomes  older  it  shades  the  ground  very  completely,  and, 
consequently,  baking  of  the  soil  is  not  so  common  later 
in  the  season. 

155.  Method    of   irrigating   wheat. — Water   may   be 
applied  to  wheat  by  any  of  the  standard  methods  of  irri- 
gation.   In  the  beginning  of  American  irrigation,  flooding 
was  almost  the  only  method  employed.    Only  gradually, 
to  meet  compelling  conditions,  was  the  furrow  method 
thought  out  and  adopted  and,  even  today,  flooding  is  the 
most  general  method  of  irrigating  wheat  and  other  small 
grains.    The  flooding  of  grain  is  accomplished  ordinarily 
by  the  field-ditch  method.    From  the  main  supply  ditch, 
smaller  ditches,  often  following  the  high  lines  or  ridges, 
are  taken  out  to  the  field.    From  these  again,  small  tem- 
porary field  ditches  or  mere  furrows  are  made,  from  which 
the  water  overflows  to  cover  the  land.    Occasionally,  but 


244 


IRRIGATION  PRACTICE 


only  where  there  is  an  abundance  of  water,  the  small 
grains  are  irrigated  by  the  check  or  basin  system.  The 
furrow  method  of  irrigating  the  small  grains  is  rapidly 
coming  into  use,  and  promises  to  displace  the  more 
extensively  used  flooding  methods.  Under  the  flooding 
method,  much  labor  is  required  to  apply  the  water  to  the 
land,  but  little  labor  to  prepare  the  land  for  irrigation. 
Under  the  furrow  method  little  labor  is  needed  to  apply 
the  water,  but  the  land  must  be  carefully  prepared  before 
the  method  can  be  employed. 

The  method  to  be  chosen  depends  on  the  soil  and  the 
scarcity  of  water.   Lands  with  a  baking    tendency,  sown 


FIG.  58.  Irrigating  wheat. 

to  grain,  as  already  suggested,  are  cultivated  with  diffi- 
culty. When  the  furrow  method  is  employed  on  such 
lands,  only  the  soil  touched  by  the  water  in  the  furrows 
bakes,  and  cultivation  is  not  so  necessary.  Other  lands 
wash  easily.  They  are  usually  of  very  fine  texture,  and 
are  rich  either  in  calcium  sulphate  with  other  somewhat 


IRRIGATION  OP  CEREALS 


245 


soluble  substances  or  are  derived  from  volcanic  ash.  Even 
a  small  stream  of  water,  with  a  slight  fall,  running  on 
such  soils,  unless  watched  with  extreme  care,  may  quickly 
cut  deep  ravines  and  destroy  the  field.  On  such  soils,  there- 
fore, the  furrow  method,  which  permits  of  a  better  con- 


*** 


FIG.  59.  Canvas  dam  to  check  water. 

trol  of  water,  is  gradually  becoming  the  only  method. 
Limited  supplies  of  irrigation  water  also  demand  the  fur- 
row method,  for  it  is  evident  that,  with  a  given  quantity 
of  water,  more  land  may  be  covered  by  the  furrow  than 
by  the  flooding  method.  It  has  been  explained  that  the 
yield  of  a  crop  to  a  unit  of  water  is  greater  when  small 
quantities  are  used  and  a  larger  total  yield  will  be  obtained 
when  the  small  available  quantity  of  water  is  spread  over 
a  large  area. 

Finally,  under  the  best  flooding  system  it  is  difficult 
to  secure  an  even  distribution  of  water  over  ordinary 
lands,  which  are  not  absolutely  level.  The  furrow  method 
permits  of  a  more  even,  though  not  by  any  means  per- 
fectly even  distribution.  This  has  been  another  determi- 
ning factor  in  the  acceptance  of  furrow  irrigation  for  small 
grains. 


246  IRRIGATION  PRACTICE 

The  furrows  are  usually  made  after  seeding  but  before 
the  plants  come  up,  by  the  use  of  special  implements 
described  in  Chapter  XX.  Shallow  furrows,  usually  5 
inches  deep  and  from  6  inches  to  3  feet  apart,  are  ordi- 
narily employed.  Their  length  varies  from  150  to  600  feet, 
depending  on  the  slope,  the  nature  of  the  soil  and  various 
other  conditions.  Long  furrows  are  of  doubtful  value, 
for  the  upper  end  of  the  furrow  receives  water  for  a  longer 
time  than  does  the  lower  end,  and,  consequently,  in  long 
furrows  the  upper  end  may  be  over-irrigated  when  the 
lower  end  has  received  just  enough.  Shorter  furrows 
obviate  this  danger,  at  least  in  part.  (Figs.  58,  59.) 

156.  Time  of  irrigating  wheat. — The  time  of  irriga- 
tion, one  of  the  most  important  factors  in  the  economical 
use  of  water,  depends  in  part  upon  the  distribution  of  the 
rainfall  throughout  the  year.  Land  for  spring  grain  is 
especially  suitable  for  fall  and  winter  irrigation.  Such 
lands,  when  plowed  in  the  early  fall  and  given  a  good 
soaking  in  the  fall,  will  contain  much  stored  water  in  the 
spring  to  germinate  the  seed  and  to  maintain  the  young 
plants  far  into  the  early  summer.  However,  fall  and  win- 
ter irrigation  is  to  be  considered  only  when  the  natural 
winter  precipitation  is  insufficient  to  saturate  the  soil  to 
a  depth  of  8  to  10  feet.  It  is  especially  in  districts  where 
the  precipitation  comes  largely  in  spring  and  the  growing 
season,  and  where  the  winter  and  fall  are  dry,  that  irri- 
gation during  the  dormant  season  is  of  much  value. 

When  the  soil  enters  the  spring  in  a  somewhat  dry  con- 
dition, it  becomes  necessary  to  provide  by  irrigation  the 
water  needed  for  germinating  the  seed.  This  may  be 
accomplished  by  applying  a  thorough  irrigation  to  the 
soil  before  seeding,  after  which  the  land  is  plowed, 
then  sown  to  the  crop.  The  objection  to  this  method  is 


IRRIGATION  OF  CEREALS  247 

the  delay  occasioned  by  the  necessary  interval  between 
irrigation  and  plowing.  For  that  reason,  the  soil  is  fre- 
quently plowed  early  in  the  spring,  irrespective  of  dry- 
ness,  the  seed  planted  in  the  dry  soil,  and  then  irrigated. 
The  water  thus  added  immediately  favors  germination 
and  furnishes  also  a  supply  of  water  for  the  young  plant. 
Both  of  these  methods  of  early  irrigation  are  giving  satis- 
factory results. 

After  germination  and  first  growth,  irrigation  should  be 
delayed  as  long  as  possible.  When  water  is  needed,  the 
grains,  which  normally  are  of  a  light  green  color,  become 
darker  green,  and  in  protracted  dryness  the  lower  leaves 
become  definitely  yellow.  If  the  soil  becomes  too  dry, 
the  crop  may  be  permanently  injured;  in  fact,  the  soil 
below  the  surface  should  remain  fairly  moist  throughout 
the  growing  season.  If  the  seed  has  been  planted  in  well- 
saturated  soil,  since  young  plants  require  little  moisture, 
several  weeks  will  elapse  before  irrigation  will  be  necessary. 

During  the  early  stages  of  growth,  the  plant  devotes 
its  energies  to  the  preparatory  work  of  gathering  carbon 
from  the  air  and  mineral  matters  from  the  soils,  and  of 
combining  these  into  organic  forms.  The  period  of  most 
rapid  growth  comes  shortly  before  or  at  the  time  of  flower- 
ing. At  the  time  of  "boot,"  that  is,  when  the  heads  just 
begin  to  show,  it  is  well  to  apply  water,  and  again,  if 
needs  be,  at  the  time  of  seed-formation.  It  is  most  impor- 
tant, however,  that  the  soil  be  not  dry  at  the  time  of 
flowering;  for,  if  there  is  an  abundance  of  water  at  that 
time,  a  ready  transfer  of  nutritive  materials  from  stalks 
and  leaves  to  the  heads  is  made  possible.  Moreover, 
water  applied  when  the  seeds  are  "filling  out"  will  result 
in  increased  grains  at  the  expense  of  the  straw. 

It  may  be  that  the  answer  to  the  question  concerning 


248  IRRIGATION  PRACTICE 

the  right  time  of  applying  water  to  grain  is  to  keep  the 
soil  approximately  at  the  same  moisture  content  through- 
out the  season,  until  ripening  sets  in.  Some  authorities 
have  declared  that  plants  need  a  high  soil-moisture  per- 
centage at  one  period  and  a  smaller  one  at  another  period 
and  so  on  throughout  the  season.  This  may  be  correct, 
but  in  practice  the  farmer  will  make  no  mistake  in  main- 
taining the  soil  in  approximately  the  same  correct  mois- 
ture condition  throughout  the  season.  More  water  will 
be  transpired,  and  the  irrigations  therefore  heavier  or 
more  frequent  at  the  time  of  most  rapid  growth,  that  is, 
about  the  time  of  flowering. 

It  is  seldom  necessary  to  give  wheat  more  than  three 
irrigations  except,  possibly,  in  the  hot  climate  of  Arizona 
and  similar  regions.  In  fact,  two  irrigations  are  usual,  and 
one  irrigation  ordinarily  ample  wherever  the  annual 
precipitation  is  between  12  and  15  inches.  Where  the 
annual  precipitation  is  large,  little  water  will  be  required; 
where  it  is  small,  much  water  must  be  added  by  irriga- 
tion. Bark  found  that  under  a  rainfall  of  about  18  inches, 
the  water  used  for  grains  by  farmers  during  the  months 
of  May  to  August  inclusive,  was  as  follows:  May,  7.86 
per  cent;  June,  52.34  per  cent;  July,  36.14  per  cent; 
August,  3.66  per  cent;  total,  100  per  cent.  In  the  moun- 
tain country,  where  grain  is  sown  in  April,  there  is  little 
need  of  irrigation  after  late  June  or  earliest  July.  Fall- 
sown  grain,  with  proper  tillage,  needs  probably  only  one 
heavy  irrigation,  or  at  the  most  two  light  irrigations. 
McLaughlin  recommends  that  wherever  weeds  have  been 
troublesome  the  grain  fields  be  irrigated  after  harvest,  to 
germinate  the  weed  seeds,  and  later  to  plow  the  plants 
under.  Thus,  the  soil  is  fertilized  and  the  weeds  destroyed. 

157.  Quantity  of  water  for  wheat. — The  quantity  of 


IRRIGATION  OF  CEREALS  249 

water  to  be  used  for  wheat  and  the  small  grains  depends 
upon  many  factors.  Less  water  is  required  on  clayey 
than  on  sandy  or  gravelly  soils.  Deep  soils  require  less 
water  than  shallow  soils,  or  soils  underlaid  by  gravel  or 
hardpan.  Bark,  working  in  Idaho,  found  that,  in  actual 
practice,  grains  received  on  medium  clays  and  sandy 
loams  about  18  inches  of  water,  while  on  sands  or  gravelly 
soil  nearly  36  inches  were  used.  More  water  is  necessary 


FIG.  60.  Irrigated  wheat  in  Montana. 


on  new  than  on  old  land.  A  high  temperature,  a  low 
relative  humidity  and  a  steady  wind  increase  the  water 
requirements  of  crops.  All  these  and  others  previously 
discussed,  must  be  considered  in  deciding  on  the  quantity 
of  water  to  be  used. 

The  fundamental  law  to  be  considered  in  determining 
the  quantity  of  water  used  in  the  production  of  wheat  and 
of  other  crops  is  that,  as  more  water  is  applied  to  a  field 
the  smaller  is  the  relative  yield  of  grain  and  of  straw. 
Undoubtedly,  as  water  is  applied,  the  total  yield  increases 


250 


IRRIGATION  PRACTICE 


steadily  to  a  limit,  beyond  which  there  is  an  actual 
decrease;  but,  as  the  increase  goes  on,  there  is  a  steady 
diminution  in  the  yield  per  unit  of  water  applied.  This  is 
shown  in  the  following  table,  taken  from  the  Utah  results: 

YIELDS   OF   WHEAT  WITH   VARYING   QUANTITIES   OF   IRRIGATION 

WATER 


Inches 
of  irrigation 
water  applied 

Bushels  of 
grain 
to  the  acre 

Pounds  of 
straw 
to  the  acre 

Pounds  of 
straw  for 
each  bushel 
of  grain 

Bushels  of 
wheat  for 
each  inch 
of  water 

5.0 

|     37.81 

2,986 

79 

7.56 

7.5 

41.54 

3,301 

75 

6.39 

10.0 

43.53 

3,452 

79 

4.35 

15.0 

45.71 

3,954 

87 

3.05 

25.0 

46.46 

4,311 

93 

1.86 

35.0 

48.55 

4,755 

98 

1.39 

50.0 

49.38 

5,332 

108 

0.99 

The  quantity  of  water  applied  to  wheat  varied  from 
5  to  50  inches,  but  the  yield  varied  from  about  thirty- 
eight  bushels  to  a  little  over  forty-nine  bushels — an 
increase  of  not  quite  twelve  bushels  of  wheat  for  an 
increase  of  nearly  45  inches  of  water.  In  the  last  column 
of  the  table,  it  is  shown  that  the  yield  per  inch  of  irriga- 
tion water  fell  from  about  seven  and  one-half  bushels  with 
5  inches  of  water,  to  about  one  bushel  with  50  inches 
of  water.  This  variation  in  yield,  due  to  increasing  applica- 
tions of  water,  has  been  confirmed  by  practically  every 
investigator  who  has  carried  on  accurate  work  under 
field  conditions.  Moreover,  the  greater  the  quantity  of 
water  used,  the  smaller  the  proportion  of  seed  in  the  whole 
plant.  See  the  fourth  column  of  the  above  table.  (Fig.  63.) 

Not  only  is  it  possible  to  diminish  beyond  serious  con- 
sideration the  acre-inch  yield  by  increasing  irrigations, 
but  it  is  possible  by  excessive  irrigation  to  cause  an  actual 


IRRIGATION  OF  CEREALS 


251 


decrease  in  the  total  yield.  Further,  an  excess  of  water 
delays  ripening,  and  thus  subjects  the  grain  to  the  dangers 
of  late  growth  when  the  fall  frosts  are  at  hand.  When  too 
much  water  is  used,  the  plant  becomes  converted  into  a 
pumping  system,  having  for  its  purpose  the  ridding  of  the 
soil  of  the  injurious  excess  of  moisture.  Such  over-irriga- 
tion is,  naturally,  less  likely  to  occur  on  porous  than  on 
compact  soils;  but,  on  the  other  hand,  the  excess  of  water 


FIG.  61.  Irrigated  oats  in  Montana. 

applied  to  porous  soils  moves  downward  more  easily  tot\ 
raise  the  standing  water  table.  Fortunately  for  the 
pioneers  who  laid  the  foundations  of  irrigation,  and  who 
were  not  well  acquainted  with  the  dangers  of  over-irriga- 
tion, the  small  grains  endure  fairly  well  an  excess  of 
water.  Wheat  can  probably  endure  over-irrigation  better 
than  either  oats  or  barley.  However,  the  practice  is  un- 
wise; and  the  ridiculously  large  quantities  of  water  often 
applied  in  the  hope  of  large  yields  are  a  serious  menace 
to  the  permanence  of  irrigation  agriculture. 


252 


IRRIGATION  PRACTICE 


The  quantity  of  water  which  produces  the  largest 
yield  of  grain  to  the  acre  is  seldom  the  most  economical 
quantity  to  apply.  In  the  irrigated  region,  the  acre  of 
land  and  the  acre-foot  of  water  must  both  be  given  atten- 
tion; and,  since  the  acre-foot  of  water  usually  has  a  higher 
value  than  the  acre  of  land,  the  emphasis  should  be 
placed  upon  the  producing  power  of  a  given  volume  of 
water.  The  possibility  of  wheat-production  with  30 
acre-inches  of  water — the  quantity  often  assigned  by 
irrigation  engineers — based  on  the  preceding  table,  may 
be  shown  as  follows: 


30  acre-inches  spread  over 

1  acre 

2  acres 

3  acres 

4  acres 

6  acres 

Grain  .    ... 

47.51 
4,532 

91.42 
2,908 

130.59 
10,256 

166.16 
13,204 

226.16 
17,916 

Straw  

By  spreading  30  acre-inches  over  6  acres  instead  of 
over  1,  the  total  yield  of  wheat  was  increased  from  forty- 
seven  bushels  to  226  bushels.  In  the  final  establishment 
of  empires  on  irrigated  soils  this  fundamental  relation- 
ship between  water  and  crop-yield,  must  of  necessity  be 
taken  into  consideration.  (Fig.  64.) 

The  best  knowledge  of  the  day  makes  it  safe  to  say 
that,  on  deep  soils,  7^  inches  of  water  in  two  good  irriga- 
tions, should  be  ample  for  the  production  of  a  crop  of 
wheat.  On  shallow,  gravelly  soils,  as  high  as  18  inches 
may  be  used  in  four  or  five  irrigations.  On  many  soils 
one  good  irrigation  of  4  to  5  inches  would  be  sufficient  to 
carry  the  crop  to  a  large  yield  of  grain  of  higher  quality 
than  if  more  water  were  used.  Everything  considered, 
an  average  of  1  acre-foot  should  be  ample  for  the  pro- 
duction of  wheat  on  fertile,  well-tilled  soils. 


IRRIGATION  OF  CEREALS 


253 


If  12  acre-inches  be  taken  as  the  quantity  of  water 
amply  sufficient  for  the  needs  of  wheat,  the  subjoined 
table  shows  that  1  second-foot,  during  a  sixty-day  irri- 
gation period,  will  cover  120  acres;  during  a  forty-five- 
day  irrigation  period,  90  acres.  If  7J^  inches  be  the 
depth  of  water  applied,  the  duty  of  a  second-foot  will 
vary  as  shown  below  from  60  to  192  acres.  In  many 
places  in  the  West,  the  duty  of  water  for  grain  has  been 
raised  to  200  acres  or  more.  For  instance,  under  the 
famous  Bear  River  Canal  of  Utah,  where  irrigation  prac- 
tices have  been  worked  out  to  great  perfection,  Wheelon 
reports  that  there  is  a  gradually  Decreasing  duty  of 
water  for  grain  and  for  all  other  crops.  At  the  present 
time  the  duty  of  water  there  approximates  170  acres  for 
grain  with  a  prospect  of  a  rapid  increase. 

DUTY  IN  ACRES  OF  SECOND-FOOT  OF  WATER  CONTINUOUSLY 
FLOWING 


Depth  of  water 
applied 

Length  of  irrigation 
season 

Duty 

7.5  inches 
7.5 

45  days 
60     ' 

144  acres 
192      " 

12.0       " 

120       " 

45     " 
60     " 

90     " 
120     " 

18.0       " 
18.0       " 

45     " 
60     " 

60      " 
80     " 

158.  Oats. — Oats  is  another  of  the  staple  crops  of  the 
irrigated  section.  It  has  almost  always  been  sown  hi  the 
spring,  but  the  development  of  dry-farming  has  led  to  the 
introduction  of  winter  varieties.  It  is  very  probable  that 
oats,  like  wheat,  will,  in  the  future  be  grown  chiefly  under 
dry-farming,  although  the  crop  will  find  an  important 


254 


IRRIGATION  PRACTICE 


place  in  the  rotations  for  maintaining  the  fertility  of 
irrigated  land. 

In  general,  oats  and  wheat  may  be  treated  alike.  The 
quantity  of  seed  should  be  carefully  regulated  with  respect 
to  the  available  water.  The  cultivation,  methods  and 


DRAINAGE  DITCH. 

FIQ.  62.  Plan  of  rice  irrigation. 

time  of  irrigation  are  practically  the  same  as  those  dis- 
cussed under  wheat.  The  duty  of  water  for  oats  is  about 
the  same  as  for  wheat,  although  oats  is  rather  more  sensi- 
tive than  wheat  to  over-irrigation.  Oats  of  high  quality 
may  be  grown  abundantly  by  the  moderate  appli- 
cation of  water.  We  are  quite  safe  in  saying  that  the 


IRRIGATION  OF  CEREALS  255 

duty  of  water  for  oats  should  not  be  any  lower  than 
for  wheat. 

159.  Barley. — Barley  is  also  a  valuable  crop  for  irri- 
gated lands.   Excellent  malting  barley  is  produced  under 
irrigation,  and,  in  fact,  irrigated  barley  appears  to  be  the 
best  for  malting.    The  irrigation  of  barley  conforms  with 
the  irrigation  of  wheat  or  oats.    Barley  is  even  more  sen- 
sitive than  oats   to   over-irrigation,  and  water  should, 
therefore,  be  applied  to  barley  with  great  care.    In  the 
Utah  work  it  was  found  that  the  total  yield  of  barley 
did  not  increase,  or  decrease,  after  a  depth  of  7^  inches 
of  water  had  been  applied.    In  the  Wyoming  work,  little 
increase  was  found  after  16  to  20  inches  had  been  applied 
However,  it  has  been  demonstrated  that  the  malting  value 
of  barley  decreases  when  too  much  water  is  applied  in 
irrigation.    The  duty  of  water  for  barley  should  not  be 
lower  than  for  oats  or  wheat. 

160.  Rye. — Rye  is  seldom  grown  under  irrigation,  for 
it  does  so  well  under  dry-farming  that  there  is  no  good 
reason  for  using  costly  irrigation  water  in  its  production. 

Wheat,  oats,  barley  and  rye  behave  very  much  the  same 
in  their  relation  to  water.  The  chief  difference  is  in  the  sen- 
sitiveness to  water.  Wheat  endures  more  water  than  oats, 
and  oats  more  than  barley,  and  barley  probably  more  than 
rye;  but,  practically,  the  effect  of  irrigation  on  these  crops 
is  the  same.  All  of  them  have  a  larger  proportion  of  straw 
in  the  whole  plant,  if  grown  with  much  water. 

161.  Corn. — Corn,  the  great  American  crop,  thrives 
and  yields   heavily  under  irrigation.    It  produces  more 
dry  matter  for  the  water  used  than  practically  any  other 
crop,  and,  when  drought  comes,  it  survives  and  produces 
fair  yields.    Dry-farm  corn  seldom  fails.    The  importance 
of  the  corn  crop  to  the  irrigated  region  will  increase  rapidly 


256 


IRRIGATION  PRACTICE 


as  its  behavior  under  irrigation  becomes  better  under- 
stood, and  as  dairying  and  other  forms  of  animal  hus- 
bandry develop  on  irrigated  lands. 

Corn  differs  from  the  small  grains  in  its  longer  growing, 
hence  longer  irrigating,  period.  The  details  of  prepar- 
ing the  land,  seeding  and  general  cultural  practices  are 


Wheat- 


s 


in       i 


GO 


FIG.  63.  Yield  vs.  water  (wheat). 


those  followed  in  humid  districts.  Drill  or  row  culture  is 
the  only  allowable  method  of  sowing  corn  under  irrigated 
conditions. 

Cultivation  is  as  essential  in  corn-growing  under 
irrigation  as  under  humid  conditions.  The  soil  should  be 
cultivated  immediately  after  each  irrigation,  as  soon  as 
the  soil  is  dry  enough  to  permit  the  hoe  to  be  safely 
used.  Moreover,  it  is  well  to  cultivate  the  corn  at  least 


IRRIGATION  OF  CEREALS 


257 


twice  to  four  times  between  irrigations.  By  this  method 
the  water-cost  of  the  crop  may  be  greatly  reduced.  More- 
over, thorough  cultivation  yields  a  corn  crop  having  a 
much  higher  feeding  value  than  one  which  has  received 
less  thorough  cultivation. 

Irrigation  water  is  invariably  applied  to  corn  in  fur- 
rows, although  the  flooding  methods  may  be  used.    Since 


FIG.  64.  Producing  power  of  30  acre-inches  (wheat). 

corn  is  inter-tilled,  it  is  much  more  convenient  and  satis- 
factory to  irrigate  by  the  furrow  method  and,  further, 
the  corn  plant  should  not  be  in  contact  with  water.  The 
furrow  is  dug  half  way  between  the  rows.  For  reasons 
already  discussed  the  furrows  should  not  be  made  too 
long. 

Corn  land  may  well  be  irrigated  in  the  fall  and  winter, 
if  the  natural  precipitation  during  those  seasons  is  not 
sufficient  to  saturate  the  soil  thoroughly.   The  soil  should 
Q 


258  IRRIGATION  PRACTICE 

be  well  stored  with  moisture  at  the  time  of  seeding,  and 
when  this  is  not  the  case  it  may  be  necessary,  as  in  the 
case  of  wheat,  to  give  the  soil  a  thorough  soaking  before 
planting. 

162.  Time  to  irrigate  corn. — Corn  is  planted  later 
than  the  small  grains  and  during  its  early  growth  is, 
therefore,  subjected  to  a  higher  temperature  and  more 
rapid  evaporation.  However,  the  young  plant  draws  little 
water  from  the  soil,  and  the  first  irrigation  after  seeding 
should  be  light  and  should  come  as  late  as  possible.  As 
the  plant  continues  its  growth  the  irrigations  may  be 
increased  in  quantity  and  frequency.  The  May  planting 
of  corn  means  that  July  and  the  first  half  of  August  are 
the  periods  of  most  rapid  growth  and  during  which  most 
irrigation  is  needed.  After  August  15,  less  water  is 
required;  in  fact,  it  is  questionable  if  water  should  be 
applied  to  corn  after  the  period  of  August  15  to  September 
1.  As  in  the  case  of  the  small  grains,  the  key  to  the  suc- 
cessful production  of  irrigated  corn  seems  to  be  to  keep 
the  soil  in  a  uniform  moisture  condition  throughout  the 
season.  It  is  manifestly  impossible  under  irrigated  con- 
ditions to  keep  the  soil  exactly  at  the  same  percentage  of 
moisture;  but,  by  proper  cultivation  and  irrigations  at 
correct  intervals,  the  soil  may  be  maintained  throughout 
the  season  at  a  favorable  moisture  percentage.  Excessively 
dry  and  wet  periods  should  never  follow  each  other. 

Corn,  like  the  small  grains,  should  have  at  its  disposal 
an  abundance  of  water  at  the  time  of  seed-formation.  When 
the  seed  is  ripening,  little  water  is  required;  in  fact,  in 
the  later  periods  of  growth,  water  must  be  withheld  from 
the  plant,  so  that  ripening  may  not  be  delayed.  If  little 
water  is  available  during  -the  season,  two  irrigations  are 
probably  sufficient,  and  two  are  better  than  one.  In  one 


IRRIGATION  OF  CEREALS  259 

series  of  Utah  experiments  it  was  found  that  7^  inches 
applied  in  one  irrigation  yielded  nearly  ninety-two  bushels 
of  corn;  whereas,  the  same  quantity  of  water  applied  in 
two  equal  irrigations  yielded  nearly  102  bushels  of  corn. 
When  the  two  irrigations  were  used,  there  was*a  larger 
proportion  of  seed  in  the  whole  plant,  indicating  that  an 
application  of  water  was  made  possible  at  the  time  of 
seed-formation,  and  nutritive  materials  were  probably 
transferred  to  the  ears  at  the  expense  of  the  stover.  An 
annual  precipitation  of  12  to  15  niches  coming  largely  in 
the  fall  and  spring  would  indicate  that  three  irrigations 
throughout  the  season  should  be  sufficient  to  mature  a 
good  crop  of  corn.  True,  many  farmers  apply  water  more 
frequently  than  this,  but  the  greater  number  of  irrigations 
is  of  doubtful  value.  Fewer  irrigations,  with  many  culti- 
vations, would  in  the  end  be  more  satisfactory.  When 
four  or  five  irrigations  are  applied,  about  10  per  cent  of 
the  total  water  should  be  added  in  June;  50  per  cent  in 
July;  30  to  40  per  cent  in  August,  and  about  10  per  cent  in 
September.  When  only  two  irrigations  are  applied,  per- 
haps 60  per  cent  of  the  total  should  come  early  in  July. 

163.  Quantity  of  water  for  corn. — Corn  is  not  a  water- 
loving  crop.  It  will  use  large  quantities  of  water  if  avail- 
able, but  it  does  not  demand  an  abundance  of  water  to 
produce  a  good  yield.  As  with  other  crops,  the  soil 
determines  chiefly  the  quantity  of  water  used  by  the 
corn  crop.  On  shallow,  gravelly  and  new  soils,  more  water 
is  necessary  than  on  the  deep,  clayey,  well-tilled  soils. 
The  climatic  factors  that  increase  evaporation  increase 
the  water-use  of  the  crop. 

Corn,  like  all  other  crops,  is  subject  to  the  law  that 
the  increase  in  yield  is  not  proportional  to  the  increasing 
water  supplied  by  irrigation.  The  more  water  is  used, 


260 


IRRIGATION  PRACTICE 


though  the  total  yield  be  slightly  larger,  the  less  the  yield 
to  the  unit  of  water.  The  following  table,  taken  from  the 
Utah  work,  will  illustrate  this  statement: 

YIELDS  OF  CORN  WITH  VARYING  QUANTITIES  OF  IRRIGATION  WATER 


Inches 
of  irrigation 
water  applied 

Bushels  of 
grain 
to  the  acre 

Pounds  of 
stover 
to  the  acre 

Pounds  of 
stover  to 
one  bushel 
of  corn 

Bushels  of 
grain  for 
each  inch 
of  water 

7.5 

79.14 

7,189 

91 

6.07 

10.0 

89.52 

6,007 

67 

5.80 

15.0 

93.93 

8,279 

88 

4.57 

20.0 

91.58 

8,692 

95 

3.59 

25.0 

99.16 

9.492 

96 

3.25 

30.0 

97.12 

10,390 

107 

2.73 

55.0 

96.78 

10,258 

106 

1.43 

The  depth  of  irrigation  varied  from  7^2  to  55  acre- 
inches,  but  the  acre  yield  increased  only  from  eighty  to 
ninety-seven  bushels  of  grain,  and  the  stover  showed  a 
similarly  small  increase.  The  bushels  of  grain  per  inch 
of  irrigation  water  were  six,  when  7J^  inches  of  water 
were  used;  and  only  1.43,  when  55  inches  were  used — a 
decrease  of  three-fourths.  Invariably,  also,  as  more  water 
was  used,  the  proportion  of  stover  to  grain  increased. 
(Fig.  65.) 

Thirty  acre-inches  have  been  allowed,  frequently,  by 
state  engineers  as  the  proper  quantity  of  water  to  be  used 
by  farmers.  It  may  be  calculated  from  the  above  table 
that,  when  30  acre-inches  are  applied  to  1  acre,  about 
ninety-seven  bushels  of  corn  are  obtained;  when  spread 
over  4  acres,  more  than  316  bushels  of  corn  are  produced. 
This  possible  crop-producing  power  of  water  must  be  con- 
sidered in  building  irrigated  empires.  The  best  knowledge 
of  the  day  indicates  that  12  to  15  acre-inches  are  ordi- 
narily a  very  satisfactory  depth  of  water  for  the  produc- 


IRRIGATION  OF  CEREALS 


261 


tion  of  good  crops  of  corn.  The  longer  growing  season  of 
corn  makes  necessary  more  irrigations  and  possibly  a 
larger  quantity  of  water  than  for  wheat.  Where  the  rain- 
fall is  less  than  12  inches,  or  on  unfavorable  soils,  or  under 
conditions  of  very  high  evaporation,  it  may  be  necessary 
to  increase  this  quantity  of  water  to  18  inches.  It  is  more 
likely,  however,  that  on  deep  soils,  properly  cultivated, 
the  depth  of  water  necessary  to  produce  proper  crops  of 
corn  may  be  reduced  to  10  or  even  7J/2  inches  of  water. 

If  it  be  assumed  that  the  length  of  the  irrigating  sea- 
son for  corn  is  ninety  days,  the  duty  *of  a  second-foot 
should  not  be  greatly  different  from  that  of  wheat.  One 


Com 


X 


20 


mnm 

1 1 1  • 


FIG.  65.  Yield  vs.  water  (corn). 


262 


IRRIGATION  PRACTICE 


second-foot,  flowing  for  ninety  days,  will  cover  180  acres 
to  a  depth  of  12  inches.  This  corresponds  closely  to  the 
duty  of  water  as  given  for  wheat.  As  in  the  case  of  the 
small  grains,  the  duty  for  corn  is  steadily  increasing. 


FIG.  66.  Irrigated  corn  in  Arizona. 

164.  Rice. — Rice  is  a  semi-tropical  plant,  best  devel- 
oped in  moist  climates.  Certain  varieties  of  upland  rice 
thrive  in  dry  climates,  but  these  are  practically  unknown 
in  the  United  States.  The  rice  of  commerce  requires 
moist  conditions,  and,  therefore,  heavy  irrigation.  It  is 
grown  chiefly  on  the  delta  and  marsh  lands  of  the  South 


IRRIGATION  OF  CEREALS  263 

Atlantic  States,  the  alluvial  lands  along  the  Mississippi, 
and  in  southwest  Louisiana  and  southeast  Texas.  Upland 
rice  may  be  grown  wherever  corn  does  well,  and  by 
methods  similar  to  those  used  in  the  culture  of  summer 
oats. 

Rice  fields  are  divided  by  field  levees  into  tracts  of 
varying  sizes,  depending  on  the  slope  of  the  land  and  the 
depth  of  water  to  be  applied.  When  the  water  is  to  stand 
over  the  field  from  6  to  12  inches  deep,  the  levees  are 
made  from  12  to  18  inches  high;  they  should,  hi  fact,  be 
just  high  enough  to  retain  the  water  at  the  depth  decided 
on.  If  the  levees  are  too  large,  the  resulting  vegetation  on 
them  is  a  source  of  annoyance.  The  method  of  irrigation 
is  necessarily  the  method  of  checks. 

Immediately  after  seeding,  the  land  is  flooded  for  a 
few  days.  When  the  plants  are  6  to  10  niches  high,  they 
receive  the  first  irrigation.  From  that  time  the  water  is 
made  to  stand  on  the  land  to  a  depth  of  3  to  6  niches  until 
the  grain  is  in  the  dough,  or  about  two  weeks  before  har- 
vest, when  the  water  is  drained  off  and  the  crop  left  to 
ripen.  The  irrigation  water  is  nearly  always  pumped  from 
lower  levels  into  the  checks,  and  the  ground  water  is 
very  near  the  surface,  so  that  it  is  not  a  difficult  matter 
to  keep  water  standing  on  the  soil  for  any  desired  length 
of  time.  The  length  of  the  irrigation  season  varies  from 
two  to  three  months,  with  an  average  of  about  seventy 
days. 

It  might  be  supposed,  from  the  fact  that  rice  fields  are 
thus  covered  with  standing  water,  that  large  quantities  of 
water  are  necessary  for  rice-production.  The  careful 
investigations  of  the  Office  of  Experiment  Stations  show 
that  only  from  12  to  18  inches  of  water  above  the  rainfall 
are  really  used  by  the  plant.  In  one  series  of  experiments, 


264  IRRIGATION  PRACTICE 

about  29  acre-inches  of  water  were  applied  throughout 
the  season  to  the  field,  including  the  rainfall ;  the  evapora- 
tion was  about  16  inches,  leaving  13  inches  that  were 
actually  used  by  the  plant.  This  is  not  greatly  different 
from  the  quantity  of  water  actually  supplied,  by  irriga- 
tion, to  other  cereals. 

The  rice  industry  is  very  old  in  the  United  States. 
For  many  years  it  had  languished,  but  of  recent  years 
has  appeared  to  show  signs  of  new  growth.  It  is  probable 
that  the  study  of  varieties  of  rice  suitable  for  growth  on 
the  great  irrigated  areas  of  the  country,  where  less  water 
must  be  used,  may  develop  another  highly  profitable 
branch  of  industry  for  the  irrigated  region.  (Fig.  62.) 

REFERENCES 

BARK,  DON  H.  Duty  of  Water;  Investigations  (1910-12).  Ninth 
Biennial  Report,  State  Engineer  of  Idaho  (1912). 

BOND,  FRANK,  and  KEENEY,  GEORGE  H.  Irrigation  Of  Rice  in  the 
United  States.  United  States  Department  of  Agriculture,  Office 
of  Experiment  Stations,  Bulletin  No.  113  (1902). 

HARRIS,  F.  S.  The  Irrigation  and  Manuring  of  Corn.  Utah  Experi- 
ment Station,  Bulletin  (1914). 

HUMBERT,  EUGENE  P.  Wheat-growing  Under  Irrigation.  New  Mex- 
ico Experiment  Station,  Bulletin  No.  84  (1912). 

HUNT,  THOMAS  F.  The  Cereals  in  America.  Orange  Judd  Company 
(1904). 

MCLAUGHLIN,  W.  W.  Irrigation  of  Grain.  United  States  Depart- 
ment of  Agriculture,  Farmers'  Bulletin  No.  399  (1910). 

MCLAUGHLIN,  W.  W.,  and  MORGAN,  E.  R.  Irrigation  Investigation 
during  1905-6.  Utah  Experiment  Station,  Bulletin  No.  99 
(1906). 

NOWELL,  HERBERT  T.  Irrigation  of  Barley.  Wyoming  Experi- 
ment Station,  Bulletin  No.  77  (1908). 

TEELE,  R.  P.  Review  of  Ten  Years  of  Irrigation  Investigations. 
United  States  Department  of  Agriculture,  Office  of  Experi- 
ment Stations,  Annual  Report  for  1908  (separate). 


IRRIGATION  OF  CEREALS  265 

WELCH,  J.  S.  Irrigation  Practice.  Idaho  Experiment  Station,  Bul- 
letin No.  74  (1914). 

WIDTSOE,  J.  A.,  and  MERRILL,  L.  A.  Methods  for  Increasing  the 
Crop-producing  Power  of  Irrigation  Water.  Utah  Experiment 
Station,  Bulletin  No.  118  (1912). 

WIDTSOE,  J.  A.,  and  MERRILL,  L.  A.  The  Yields  of  Crops  with 
Different  Quantities  of  Irrigation  Water.  Utah  Experiment 
Station,  Bulletin  No.  117  (1912). 


CHAPTER  XIV 

ALFALFA   AND  OTHER   FORAGE   CROPS   AND 
PASTURES 

A  PERMANENT,  modern  system  of  agriculture  cannot 
be  developed  without  the  aid  of  live-stock  husbandry. 
Consequently,  forage  crops  and  pastures  are  of  high 
importance  in  irrigation  agriculture.  However,  no  forage 
crops  of  any  kind  should  be  shipped  out  of  the  dis- 
trict where  they  are  raised,  for  the  plant-food  contained 
in  hays,  especially  alfalfa  hay,  is  often  worth  more  than 
the  money  actually  received  for  the  hay.  Irrigation- 
farmers,  dealing  with  a  new  and  largely  undeveloped 
system  of  agriculture,  on  very  fertile  soils,  are  tempted 
to  pay  little  or  no  attention  to  the  permanence  of  the 
system.  In  the  sections  recently  reclaimed  by  irrigation, 
there  is,  however,  the  most  unusual  opportunity  known 
in  the  history  of  agriculture,  to  apply  our  vast,  new  agri- 
cultural knowledge  on  lands  which  never  before  have 
been  under  cultivation.  It  should  be  possible  by  the  wise 
use  of  our  knowledge  to  build,  under  irrigation,  a  system 
of  agriculture  excelling  all  others  in  profitableness  and 
increasing  fertility.  A  first  principle  in  accomplishing 
this  is  that  the  irrigated  sections  must  send  out  only  such 
products  as  have  been  manufactured  from  the  rougher 
crops — butter,  cheese,  sugar  and  meats — and  which  con- 
tain the  minimum  quantities  of  plant  nutrients. 

165.  Alfalfa,  or  lucern. — This  wonderful  crop  has 
been  the  foundation  of  successful  irrigation  agriculture 

(266) 


ALFALFA,  FORAGE  CROPS  AND  PASTURES      267 

in  the  United  States.  If  corn  is  the  king,  then  alfalfa  is 
the  queen  of  American  crops.  Alfalfa  is  of  high  antiquity, 
and  the  watchful  care  of  unnumbered  generations  of 
farmers  has  resulted  in  a  crop  of  extremely  high  agri- 
cultural value.  It  thrives  best  in  arid  and  semi-arid 
climates,  and  under  irrigation  in  such  climates  reaches 
its  highest  perfection.  Differences  in  altitude  or  average 
temperature  do  not  affect  it  much,  so  that  over  the  whole 
irrigated  section,  from  the  high  mountain  valleys  to  the 
seacoast  and  from  the  cold  mountain  country  to  the  burn- 
ing sands  of  the  low  desert,  alfalfa  thrives  and  yields 
heavily.  It  is  an  excellent  preparatory  crop  for  infertile 
or  new  land.  In  cases  without  number  it  has  been  found 
that  lands  on  which  grain  would  not  at  first  grow  would 
support  alfalfa,  and  that,  after  some  years  hi  this  crop, 
the  lands  would  produce  grams  or  any  other  crop.  It  is 
a  host  for  nitrogen-gathering  forms  of  life  and,  therefore, 
increases  the  fertility  of  the  soil.  It  is  a  most  palatable 
food  for  all  domestic  animals,  which  thrive  upon  it.  Its 
tonnage  is  large,  averaging  about  five  tons  to  the  acre.  It 
is  reported  that  in  Arizona  and  similar  districts,  excep- 
tional yields  of  seven  tons  or  more  are  obtained.  With 
proper  tillage,  an  alfalfa  field  lasts  long.  Even  with  the 
improper  tillage  given  the  early  alfalfa  fields  of  the  West, 
there  are  fields,  forty  to  fifty  years  old,  that  are  still 
yielding  large  harvests.  When  the  alfalfa  field  is  disked  or 
harrowed  annually,  it  should  continue  for  generations  to 
produce  undiminished  yields. 

Alfalfa  requires  abundant  sunshine,  and  prefers  a  high 
summer  temperature.  It  does  best  on  rich,  deep,  well- 
drained  soil.  Hardpan  or  ground  water  near  the  surface 
is  undesirable,  as  it  tends  to  prevent  the  descent  of  the 
tap-root.  Especially  is  such  interference  objectionable 


268  IRRIGATION  PRACTICE 

when  it  comes  after  the  plant  has  developed  roots  deeply 
iii  the  soil.  It  is  not  an  ideal  dry-farm  crop  except  where 
the  ground  water  is  within  reach,  so  that  the  roots  may 
draw  water  from  below.  It  is  essentially  an  irrigated  crop, 
and  thrives  best  where  the  conditions  of  soil,  tempera- 
ture, relative  humidity  and  sunshine  are  of  an  arid 
character. 

There  is  nothing  unusual  in  the  preparation  of  land 
for  alfalfa.  It  requires  a  smooth  surface  preferably  with 
a  slope  of  from  10  to  20  feet  to  the  mile.  It  should  be 
sown  in  drill  rows  on  land  well  stored  with  water.  It  is 
difficult  to  obtain  a  stand  on  raw  land.  Oats  may  be  sown 
with  it  as  a  nurse  crop.  During  the  first  two  years  of  its 
life  it  needs  careful  culture.  By  that  time  it  is  well  estab- 
lished and  can  then  receive  the  regular  treatment  given 
the  matured  alfalfa  fields.  Water  should  then  be  kept 
off  the  land  until  it  is  actually  needed,  so  that  the  plant 
roots  may  be  trained  to  strike  deeply. 

166.  Cultivation  of  alfalfa. — Cultivation  of  alfalfa 
fields  to  prevent  the  evaporation  of  water  is  very  possible. 
Each  fall  the  alfalfa  field  is  gone  over  with  a  disk  or  a 
harrow,  which  loosens  the  top  soil  to  prevent  evaporation, 
and,  at  the  same  time,  leaves  the  soil  so  that  it  may  easily 
absorb  water  and  be  acted  on  by  atmospheric  agencies. 
Meanwhile,  the  thoroughness  with  which  the  older  plant 
shades  the  ground  tends  greatly  to  diminish  evaporation. 

It  is  a  very  common  practice,  after  the  last  cutting, 
to  turn  cattle  and  horses  into  the  alfalfa  field,  to  make  use 
of  the  late  growth.  When  pastures  are  scarce,  and  hay 
not  abundant,  this  may  be  justifiable,  but,  considering 
the  effect  upon  the  field,  it  is  of  doubtful  value.  The 
tramping  of  the  animals  makes  the  soil  hard  and  if  there 
are  fall  rains,  the  top  soil  may  become  puddled  and  thus 


ALFALFA,  FORAGE  CROPS  AND  PASTURES      269 

the  alfalfa  seriously  injured.  If  such  pasturing  is  not  fol- 
lowed by  disking,  there  may  be  a  great  diminution  in  the 
value  of  the  field.  Occasionally,  stock  is  turned  into  the 
field  after  each  cutting.  The  practice  must  be  wholly 
abandoned.  It  is  also  important  that  stock  be  kept  off  the 
field  soon  after  an  irrigation.  The  top  soil  of  alfalfa,  as  of 
the  grains;  must  be  kept  in  an  ideal  condition  for  plant- 
growth. 

167.  Method  of  irrigating  alfalfa. — Water  may  be 
applied  to  the  alfalfa  field  either  by  flooding  or  furrowing. 
If  water  is  abundant,  flooding  is  generally  the  method 
employed.  Check  or  border  irrigation  has  been  used  on  a 
large  scale  with  alfalfa  fields. 

The  border  method  uses  sections  of  the  field,  about  15 
feet  wide,  of  varying  width  up  to  900  feet  long.  The  bor- 
der levees  are  about  7  feet  wide  and  1  foot  high,  and 
covered  with  alfalfa.  Water  is  run  down  in  a  large  sheet 
between  these  levees.  The  check  method  completely 
incloses  large  fields  of  alfalfa  with  levees,  into  which  the 
water  is  run  until  it  covers  the  whole  field  to  a  certain 
depth.  In  the  inter-mountain  region,  on  the  smaller 
fields,  where  the  flooding  method  is  followed,  water  is 
applied  by  the  field-ditch  method.  From  the  supply 
ditch,  a  transverse  ditch  is  run  to  the  field,  from  which 
the  water  is  spread  over  the  soil  by  means  of  small  field 
furrows  that  do  not  interfere  materially  with  the  plant 
or  its  harvesting. 

Recently  the  furrow  method  promises  to  displace  the 
flooding  method  for  irrigating  lucern  fields.  Where  the 
soil  tends  to  run  together,  or  where  it  bakes  hard  after 
irrigation,  the  furrow  method  is  especially  employed. 
Where  the  supply  of  water  is  limited,  it  has  been  found 
advisable  also  to  employ  the  furrow  method.  In  furrowing, 


270 


IRRIGATION  PRACTICE 


the  land,  immediately  after  seeding,  is  "laid  off,"  ''marked" 
or  furrowed.  The  furrows  thus  made  become  permanent, 
and  last  usually  as  long  as  the  field  is  used.  They  may 
become  partly  filled  from  year  to  year  with  the  sediment 
carried  by  irrigation  water,  but  this  is  removed  by  the 
annual  cleaning.  The  method  of  applying  water  by  fur- 
rows is  the  same  for  alfalfa  as  for  other  crops.  (Fig.  67.) 


i 


FIG.  67.  Plan  of  irrigating  an  alfalfa  field  in  Colorado. 


Perhaps  5  per  cent  of  the  total  irrigated  area  of  alfalfa 
is  sub-irrigated  by  natural  means,  as  already  explained. 

168.  Time  to  irrigate  alfalfa. — If  the  fall  and  winter 
rainfall  is  insufficient  to  saturate  the  soil,  fall  or  winter 
irrigation  of  alfalfa,  especially  if  the  winters  are  mild  and 
open,  has  been  found  quite  satisfactory.  It  is  imperative, 
however,  that  water  applied  to  alfalfa  in  the  fall  or  winter 
be  made  to  soak  into  the  soil,  for  if  water  stands  on  the 
soil,  in  winter,  the  crop  will  probably  be  injured.  Water 
should  not  be  applied  in  the  fall  until  some  time  after 


ALFALFA,  FORAGE  CROPS  AND  PASTURES      271 

the  last  harvest,  when  the  plants  are  dormant.  Open, 
dry  winters  are  not  conducive  to  good  alfalfa  yields.  A 
soil  of  low  water  content  in  winter  is  not  so  satisfactory  for 
alfalfa  as  one  that  is  near  field  saturation.  However,  too 
much  water  is  equally  harmful,  and  may  cause  winter- 
killing. Free  water,  found  in  the  upper  foot  or  two  of  the 
soil,  freezes  in  seasons  of  high  cold,  and  serious  injury 
is  done  the  plants.  The  alternate  freezing  and  thawing 
of  some  winters  is  even  more  injurious  to  the  crop.  If 


FlQ.  68.  Temporary  county  fair  building  constructed  of  baled  alfalfa  hay.    In  a 
pioneer  section. 

water  is  allowed  to  form  ice  over  the  surface,  the  alfalfa 
plants  are  fatally  injured.  The  soil  should  not  be  too  wet 
in  the  spring,  for  the  low  temperature  of  the  soil  induced 
by  the  presence  of  much  water  will  tend  to  retard  the 
early  and  important  spring  growth. 

After  the  spring  growth  has  begun,  the  first  irrigation 
should  be  postponed  for  some  weeks,  although  it  is  not  so 
important  to  do  this  with  alfalfa  as  with  the  annual  crops 
that  are  irrigated  late  in  order  to  drive  their  root-systems 
downward.  Where  wheat  is  planted  in  April,  the  first 


ALFALFA,  FORAGE  CROPS  AND  PASTURES      273 

irrigation  of  lucern  usually  comes  the  first  or  second  week 
in  June  and  occasionally  as  late  as  the  third  or  fourth  week 
in  June.  Little  water  in  the  soil  at  the  time  of  first  growth 
makes  it  necessary  to  apply  water  even  earlier. 

It  is  sufficient,  under  conditions  of  deep  soil  and  moder- 
ate evaporation,  to  give  the  crop  one  irrigation  for  each 
cutting;  two  or  even  three  light  irrigations  for  each  cut- 
ting are  not  objectionable.  The  best  present  practice  is 
to  apply  water  a  few  days  before  cutting  and  again  soon 
after  cutting — nearly  two  irrigations  for  each  cutting. 

If  one  irrigation  for  each  cutting  is  used,  it  is  always  a 
question  whether  to  apply  it  before  or  after  cutting.  If 
water  is  applied  just  before  the  cutting  of  alfalfa,  when  the 
land  is  covered  with  a  heavy  growth,  there  is  more  trouble 
to  cover  the  land  properly  with  water.  On  the  other 
hand,  the  water  becomes  well  distributed  throughout 
the  soil  in  time  to  serve  the  second  cutting  to  the  best 
advantage.  If  the  water  is  applied  immediately  after 
cutting,  there  is  less  trouble  hi  applying  it  to  the  clean 
field,  but  it  will  take  longer  time  before  the  plant  can  make 
as  good  use  of  the  water  as  it  could  if  it  were  already  dis- 
tributed throughout  the  soil.  In  the  Utah  work,  no  appre- 
ciable difference  in  total  seasonal  yield  was  found  whether 
the  irrigation  was  applied  just  before  or  just  after  cutting. 
Heavy  soils  bake  .more  readily  if  water  is  applied  after 
cutting. 

Bark  has  determined  the  time  at  which  alfalfa  is  irri- 
gated by  a  large  number  of  Idaho  farmers  and  the  per- 
centage of  the  season's  irrigation  applied  each  month. 
The  following  table  shows  some  of  the  results: 

Per  cent  Per  cent 

April 1.28       July 30.00 

May 20.90  August      .    .    r-**.    .    .    .      23.75 

June 16.95  September    .    .    .    ^^    .    .        4.42 

R 


274 


IRRIGATION  PRACTICE 


It  may  be  observed  that  1.28  per  cent  of  the  total 
quantity  applied  during  the  seaon,  was  added  in  April. 
That  undoubtedly  was  due  to  the  lack  of  water  in  the  soil 
at  that  time.  The  May  irrigation,  likewise,  was  doubt- 
lessly applied  to  lands  not  well  saturated  with  moisture 
in  the  spring.  The  bulk  of  the  irrigation  came  in  July 
and  August,  during  the  time  of  the  second  and  third 
cuttings. 

169.  Quantity  of  water  for  alfalfa. — The  growing  sea- 
son for  alfalfa  is  longer  than  for  the  small  grains,  but  to 
offset  this  it  uses  less  water  for  each  pound  of  dry  matter. 
Nevertheless,  the  heavier  acre-yield  of  alfalfa  makes 
necessary  more  irrigation  for  alfalfa  than  for  the  cereals. 
The  law  connecting  yield  of  alfalfa  with  the  quantity  of 
water  used  is  the  same  as  that  developed  for  other  crops. 
In  the  following  table  are  given  the  results  of  experiments 
on  the  water  requirements  of  alfalfa  conducted  by  Fortier 
in  Montana: 

YIELDS  OF  CURED  ALFALFA  HAY  WITH  VARYING  QUANTITIES  OF 
IRRIGATION  WATER 


Inches  of  irrigation 
water  supplied 

Pounds  per  acre 

Pounds  per  inch 
of  water 

6 

9,220 

1,537 

12 

8,840 

737 

18 

7,500 

416 

24 

12,700 

529 

30 

14,400 

480 

36 

15,360 

426 

The  depth  of  irrigation  water  varied  from  6  to  36 
inches;  the  total  yield  of  well-cured  alfalfa  hay,  from 
9,000  to  15,000  pounds.  As  shown  in  the  third  column  of 
the  table,  the  yield  did  not  keep  pace  with  the  increase 


ALFALFA,  FORAGE  CROPS  AND  PASTURES       275 


in  the  irrigation  water  for  the  harvest  of  cured  alfalfa  hay, 
for  each  inch  of  irrigation  water  fell  from  1,500  pounds 
when  6  inches  of  water  were  used,  to  400  pounds  when  36 
inches  of  water  were  used.  The  maximum  yield  did  not 
coincide  with  the  economic  yield.  The  results  obtained 
by  Fortier  have  been  corroborated  by  the  Utah  Sta- 
tion. Some  of  the  data  obtained  are  found  hi  the  follow- 
ing table: 

YIELDS  OF  CURED  ALFALFA  HAY  WITH  VARYING  QUANTITIES  OF 
IRRIGATION  WATER 


Inches  of  irrigation 
water  supplied 

Pounds  per  acre 

Pounds  per  inch 
of  water 

10 

9,884 

988 

15 

7,546 

503 

20 

9,097 

455 

25 

9,354 

374 

30 

8,840 

295 

50 

10,813 

216 

The  irrigation  water  applied  was  increased  from  10  to 
50  inches,  and  the  yield  of  cured  alfalfa  hay  increased 
from  9,800  to  10,800  pounds.  That  is,  the  yield  of  cured 
alfalfa  for  each  inch  of  water  fell  from  988  pounds  to  216 
pounds  as  the  irrigation  water  was  increased  five-fold. 
Bark,  working  in  Idaho,  found  the  same  law  to  hold. 
(Fig.  70.) 

While  alfalfa  does  not  respond  proportionally  to  the 
application  of  large  quantities  of  water,  yet  it  can  endure 
fairly  large  irrigations,  providing  the  soil  is  fertile  and  not 
too  heavy.  In  water-logged  soils,  the  yield  of  alfalfa  is 
invariably  lessened.  Alfalfa,  not  properly  cared  for  by 
harrowing  or  disking,  does  not  respond  well  in  its  yield  to 
the  water  used.  This  is  particularly  important  in  districts 


276 

12OOO 
CO  9OOO 


$0000 


IRRIGATION  PRACTICE 


. 


GO 


Jllfa.Ua, 


FIG.  70.  Yield  vs.  water  (alfalfa). 


M\ 


the  irrigation  water  of  which  deposits  much  silt  over 
the  soil. 

A  small  quantity  of  water  will  give  a  fair  yield  of  alfalfa 
hay;  good  returns  are  obtained  with  12  to  18  or  even  24 
inches  of  water.  In  general,  on  alfalfa  fields,  about  one 
and  one-half  times  as  much  water  may  be  safely  used  as  is 
given  to  corn  and  the  small  grains.  On  deep  soils,  alfalfa 


ALFALFA,  FORAGE  CROPS  AND  PASTURES       277 

will  take  more  water  and  give  good  returns.  The  abun- 
dance of  water  must  always  be  considered  in  determining 
the  water  to  be  used  on  alfalfa  fields,  for  it  will  determine 
whether  the  acre  yield  or  the  acre-inch  yield  is  of  first 
importance.  Fortier's  results  show  that  30  acre-inches, 
used  on  one  acre,  produce  about  14,400  pounds  of  alfalfa 
hay;  on  five  acres,  about  64,100  pounds.  It  is  probably 
safe  to  say  that,  on  the  fertile  soils  of  the  West,  not  more 
than  18  niches  of  water  need  be  applied  to  alfalfa,  provid- 
ing the  crop  is  given  good  cultivation.  On  soils  that  are 
infertile,  shallow,  very  sandy  or  underlaid  by  hardpan, 
more  can  probably  be  well  used.  This  depth  of  water 
refers  to  districts  which  receive  an  annual  rainfall  of  12  to 
15  inches.  Where  less  rain  falls,  more  water  must  probably 
be  added  in  irrigation;  where  more,  less  need  be  applied. 

The  irrigation  season  for  alfalfa  covers  approximately 
120  days — June  to  September,  inclusive.  During  this 
period  one  second-foot  will  cover  240  acres  to  a  depth  of 
12  inches;  150  acres  to  a  depth  of  18  inches;  120  acres 
to  a  depth  of  24  inches.  The  best  managed  irrigation 
systems  have  a  duty  of  water  for  alfalfa  of  about  150 
acres,  which  is  increasing. 

Irrigated  alfalfa  hay  is  of  high  quality.  The  quantity 
of  water  used  in  producing  alfalfa  determines,  in  a  large 
measure,  the  quality  of  the  hay.  The  more  water  used,  the 
more  woody  the  hay  becomes,  and  the  less  valuable, 
therefore,  for  feeding  purposes.  The  less  water  used,  the 
richer  the  hay  becomes,  per  pound,  in  the  blood-  and 
muscle-forming  elements.  All  in  all,  as  with  other  crops 
so  with  alfalfa — it  must  be  grown  with  a  moderate  quan- 
tity of  water. 

170.  Alfalfa  seed. — The  present  large  demand  for  al- 
falfa seed  is  likely  to  continue  as  long  as  new  lands  are  being 


278  IRRIGATION  PRACTICE 

brought  under  irrigation.  The  conditions  determining  the 
production  of  alfalfa  seed  are  not  well  understood,  but  the 
chief  secret  seems  to  be  the  use  of  little  water.  The  first 
cutting  is  harvested  as  usual  for  hay;  the  second  cutting 
is  allowed  to  go  to  seed  with  little  irrigation — none  if  the 
first  cutting  has  been  well  irrigated;  after  the  harvest, 
water  is  added  to  obtain,  if  possible,  a  small  third  crop. 
The  use  of  much  water  diminishes  the  yield  of  seed,  and 
also  retards  the  production  of  the  seed  until  too  late  in 
the  fall.  Morgan,  working  in  Utah,  obtained  the  highest 
yield  of  seed  when  about  8  inches  were  used.  Either  less 
or  more  resulted  in  smaller  yields  of  seed.  In  other  locali- 
ties, some  other  quantity  might  be  found  to  be  best,  but 
it  is  never  large.  Another  method  of  producing  alfalfa 
seed  is  to  clip  the  first  growth  of  alfalfa  about  the  time 
of  the  first  irrigation,  or  a  little  earlier,  and  then  to  allow 
the  first  crop  to  go  to  seed.  By  many,  this  is  held  to  be 
by  far  the  most  successful  method  of  producing  alfalfa 
seed.  The  whole  matter  needs  much  careful  experimental 
study  before  definite  rules  can  be  laid  down. 

171.  Hay-making  crops. — The  standard  hay-making 
crops  may  all  be  produced  under  irrigation.  With  the 
growth  of  irrigation  there  will  be  an  increasing  demand 
for  a  variety  of  hay-making  crops.  While  nearly  all  hay- 
making crops  will  thrive  under  irrigation,  they  do  so  with 
varying  degrees  of  success,  depending  upon  their  adap- 
tability to  the  soil  and  climatic  conditions  of  the  irrigated 
region.  Usually,  some  years  of  adaptation  precede  the 
best  results  from  any  crop  introduced  into  the  irrigated 
region. 

The  Utah  work  included  studies  of  timothy,  orchard- 
grass,  brome-grass,  and  Italian  rye-grass,  all  of  which 
are  typical  hay-making  crops.  These  were  planted  as 


ALFALFA,  FORAGE  CROPS  AND  PASTURES       279 


usual,  took  root  and  grew  well.  Plenty  of  water  was  added 
in  the  spring  to  cause  an  early  start  and  to  imitate  a  cool, 
moist  spring;  after  which  water  was  held  off  for  several 
weeks,  until  near  the  time  of  cutting.  Any  of  the  well- 
established  methods  of  applying  water  may  be  used.  From 
5  to  100  inches  were  used  in  the  experiments.  In  every 
case  there  was  a  smaller  yield  with  100  inches  than  with 
5  inches.  In  some  cases,  smaller  yields  were  obtained 
with  10  to  15  inches  than  with  5  inches.  The  evidence  of 
the  available  experimental  work  is  that  these  grasses 
tolerate  only  small  quantities  of  water.  The  following 
table  shows  some  of  the  results  obtained  hi  the  Utah  work : 

YIELD  IN  POUNDS  PER  ACRE 


Irrigation 
water  used 
in  acre-inches 

Timothy 

Orchard-grass 

Brome-grass 

Italian 
rye-grass 

5.0 

2,526 

7.5 

3,982 

.    . 

4,480 

2,'35*7 

10.0 

.    . 

2,829 

4.957 

.    . 

15.0 

3,844 

2,685 

.    . 

2,218 

30.0 

6,054 

.    . 

3,821 

.    . 

40.0 

m 

4,042 

. 

f    f 

45.0 

.    . 

. 

m    . 

60.0 

8,406 

5,270 

4^757 

3,201 

100.0 

2,214 

1,192 

3,068 

2,357 

Since  the  roots  of  these  plants  do  not  penetrate  the 
soil  deeply,  the  frequent  application  of  water  may  be 
justified,  but  the  total  quantity  need  not  be  great.  Timo- 
thy appears  to  endure  much  water  better  than  the  other 
crops.  One  crop  only  is  obtained  from  these  grasses,  and 
they  are,  therefore,  much  like  the  small  grains  in  their 
water  requirements.  Ordinarily  it  is  sufficient  to  give 
these  crops  one  good  irrigation  before  cutting.  From  5  to 
10  inches  of  water  should  be  sufficient  to  produce  the  one 


280 


IRRIGATION  PRACTICE 


crop  of  hay.  On  infertile  or  sandy  soils  from  10  to  15 
inches  should  be  ample.  Where  the  aftermath  is  pastured, 
the  field  may  be  irrigated  lightly  once  or  twice  during  the 
hot  months  of  July  and  August,  when  good  pasturage 
results  until  late  in  the  fall. 

These  and  other  grasses,  especially  the  native  grasses, 
are  often  grown  on  the  large  ranches  of  the  West.  One 
crop  is  ordinarily  harvested  and  the  aftermath  pastured. 
As  early  as  possible  in  the  spring,  these  fields  are  covered 


Fia.  71.  Flooding  pasture  land. 

with  immense  quantities  of  water,  which  often  stand  for 
days,  1  to  2  feet  deep.  It  is  believed  that  under  such  con- 
ditions the  frost  is  taken  out  of  the  soil,  and  a  larger 
quantity  of  hay  is  obtained.  The  experiments  at  our  ser- 
vice indicate  that  all  hay  crops  are  injured  by  an  excess 
of  water,  and  that  the  best  yields  are  obtained  only  by 
moderate  irrigations.  The  immoderate  use  of  water  on 
such  ranches  should  be  discontinued,  for  it  is  an  absolutely 
senseless  practice.  The  hay-making  grasses,  whether 
tame  or  wild,  should  not  be  given  too  much  water  if  large 
yields  are  desired. 


ALFALFA,  FORAGE  CROPS  AND  PASTURES      281 

172.  Red  clover. — Red  clover,  and  the  other  clovers, 
should  be  irrigated  much  as  is  the  first  cutting  of  alfalfa, 
or  the  grasses  above  discussed.  All  the  standard  forage 
crops  are  subject  to  the  laws  already  laid  down.  It  is 
probable  that  from  12  to  15  niches  would  meet  amply 
the  requirements  of  practically  any  one  of  the  standard 
hay  crops.  The  longer  the  growing  period  of  the  crop  the 
larger  will  be  the  necessary  quantity  of  water.  When 


FIG.  72.  Irrigating  young  alfalfa. 

vetches  and  peas  are  grown  for  hay  they  are  to  be  treated 
as  indicated  for  peas  in  Chapter  XV. 

173.  Pastures  and  meadows. — Many  natural  meadows 
are  supplied  with  water  from  below.  In  fact,  in  the  irri- 
gated section,  the  term  meadow  is  generally  applied  to 
natural  pastures  where  no  irrigation  is  needed.  These 
sometimes  become  dry  in  the  summer,  and  must  then  be 
irrigated.  The  time  and  quantity  of  application  depend 
entirely  upon  the  prevailing  conditions.  No  rules  can  be 
laid  down. 


282  IRRIGATION  PRACTICE 

The  chief  pastures  of  the  irrigated  region  are  those  that 
are  irrigated  throughout  the  season;  and  these  pastures 
are  the  finest  known  to  agriculture.  They  may  be  kept 
green  and  luxuriant  throughout  the  season,  and,  there- 
fore, will  support  many  times  the  head  of  live-stock  pos- 
sible on  unirrigated  pastures  of  humid  regions.  As  live- 
stock husbandry  develops  under  irrigation,  pastures  will 
rapidly  increase. 

There  is  as  yet  no  unity  in  the  practice  of  selecting 
mixtures  of  grasses  for  irrigated  pastures.  All  the  stand- 
ard pasture  grasses  are  used  in  a  variety  of  combinations 
under  irrigation.  Thus,  in  various  combinations  accord- 
ing to  soil,  climate  and  individual  views,  the  following 
are  used  on  the  irrigated  pastures  of  the  West:  Kentucky 
blue-grass,  perennial  rye-grass,  meadow  fescue,  red  clover, 
red-top,  orchard-grass,  white  clover,  alfalfa,  meadow  oat- 
grass,  brome-grass,  Rhode  Island  bent,  timothy,  alsike, 
and  many  of  the  native  grasses,  which,  as  they  become 
better  known,  will  become  important  factors  in  the 
reclamation  of  the  West.  The  proper  mixture,  culture 
and  irrigation  of  these  plants  will  give  a  constant,  free, 
luxuriant  pasturage  that  should  bring  dairying  and 
related  branches  of  live-stock  husbandry  to  their  highest 
possible  development. 

All  pastures  should  receive  fairly  heavy  irrigations  in 
the  spring,  and  if  they  are  used  throughout  the  season 
should  be  irrigated  during  the  whole  summer.  Pastures 
that  are  well  established  on  deep  soils,  should  not  be  irri- 
gated, after  the  irrigation  season  begins,  oftener  than  every 
two  weeks,  and  then  to  a  depth  of  3  to  4  inches.  If  the  pas- 
tures are  on  gravelly  or  shallow  lands,  water  must  be 
applied  perhaps  as  often  as  once  a  week,  but  in  such  cases 
less  water  should  be  applied  at  each  irrigation. 


ALFALFA,  FORAGE  CROPS  AND  PASTURES      283 

The  irrigation  season  for  pastures  is  approximately 
the  same  as  for  corn  or  potatoes.  The  largest  need  for 
water  is  in  July  and  August,  when  the  hot  weather  causes 
the  most  rapid  evaporation.  Irrigated  pastures  must  not 
be  allowed  to  become  very  dry,  for  it  is  difficult  for  the 
pasture  to  recover  in  a  season  from  a  set-back  due  to  a 
period  of  extreme  dryness.  On  the  other  hand,  the  fal- 
lacy of  over-irrigation  should  be  avoided.  Pastures  do 
not  need  much  more  water  than  do  the  hay  crops.  The 
long  growing  season,  the  shallow  root-system  and  the 
variety  of  plants  in  the  pasturage  mixture,  make  it  difficult 
to  foretell  the  best  quantity  of  water  for  pastures.  With 
our  present  knowledge,  however,  it  is  safe  to  say  that 
from  12  to  24  inches  of  water  should  be  ample  to  main- 


FIG.  73.  Irrigated  cane  in  Kansas. 


284  IRRIGATION  PRACTICE 

tain  any  well-planted  pasture  in  a  luxuriant  condition 
throughout  the  season.  This  is  a  wide  limit,  and  it  is 
probable  that  the  best  quantity  lies  near  18  inches. 

Irrigated  pastures  should  not  be  grazed  in  early  spring 
or  immediately  after  an  irrigation,  when  the  soil  is  soft, 
because  the  plants  may  then  be  materially  injured. 
Meadows  and  pastures  should  be  frequently  disked  or 
harrowed,  so  that  the  top  soil  may  be  kept  in  a  somewhat 
loose  condition.  Such  treatment  will  diminish  the  quantity 
of  water  required  throughout  the  season.  Under  the 
most  favorable  conditions,  the  constant  tramping  of 
animals  on  pastures  will  compact  the  top  soil  and  thereby 
increase  evaporation,  decrease  the  rate  of  water  penetra- 
tion and  increase  the  quantity  of  water  required  for  the 
growth  of  the  plants.  The  key  to  pasture  maintenance 
seems  to  be  the  relatively  frequent  applications  of  small 
quantities  of  water  to  prevent  any  period  of  excessive 
dryness. 

REFERENCES 

BARK,  DON  H.  Duty  of  Water;  Investigations  (1910-12).  Ninth 
Biennial  Report,  State  Engineer  of  Idaho  (1912). 

COBURN,  F.  D.  The  Book  of  Alfalfa.  Orange  Judd  Company 
(1902). 

EVANS,  M.  W.  Timothy  Production  on  Irrigated  Lands  in  the 
Northwestern  States.  United  States  Department  of  Agricul- 
ture, Farmers'  Bulletin  No.  502  (1912). 

FORTIER,  SAMUEL.  Irrigation  of  Alfalfa.  United  States  Department 
of  Agriculture,  Farmers'  Bulletin  No.  375  (1909). 

MCLAUGHLIN,  W.  W.,  and  MORGAN,  E.  R.  Report  on  Irrigation 
Investigations  during  1905-06.  Utah  Experiment  Station, 
Bulletin  No.  99  (1906). 

OLIN,  W.  H.  American  Irrigation-Farming.  A.  C.  McClurg  Com- 
pany (1913). 


ALFALFA,  FORAGE  CROPS  AND  PASTURES      285 

TEELE,  R.  P.  Review  of  Ten  Years  of  Irrigation  Investigations. 
United  States  Department  of  Agriculture,  Office  of  Experiment 
Stations,  Annual  Report  for  1908  (separate). 

WELCH,  J.  S.  Irrigation  Practice.  Idaho  Experiment  Station, 
Bulletin  No.  74  (1914). 

WESTGATE,  J.  M.,  McKEE,  ROLAND,  and  EVANS,  M.  W.  Alfalfa 
Seed-Production.  United  States  Department  of  Agriculture, 
Farmers'  Bulletin  No.  495  (1912). 

WIDTSOE,  J.  A.,  and  MERRILL,  L.  A.  The  Yields  of  Crops  with  Dif- 
ferent Quantities  of  Irrigation  Water.  Utah  Experiment  Sta- 
tion, Bulletin  No.  117  (1912). 

WIDTSOE,  J.  A.,  and  MERRILL,  L.  A.  Methods  for  Increasing  the 
Crop-producing  Power  of  Irrigation  Water.  Utah  Experiment 
Station,  Bulletin  No.  118  (1912). 

WILCOX,  Lucius  M.  Irrigation  Farming.  Orange  Judd  Company 
(1902). 

WING,  Jos.  E.    Alfalfa  Farming  in  America.    Sanders  Publishing 
Company  (1909). 


CHAPTER  XV 

SUGAR  BEETS,  POTATOES  AND 
MISCELLANEOUS  CROPS 

AMONG  the  most  satisfactory  irrigated  crops  are  those 
that  pass  through  some  process  of  manufacture  before 
they  are  placed  upon  the  market.  Thus,  sugar  beets 
reach  the  consumer  as  sugar;  potatoes,  often  as  starch; 
hay  as  butter  or  cheese;  fiber  crops  as  twine  and  rope;  oil 
crops  as  oil,  and  so  on.  It  must  be  the  great  endeavor  of 
irrigation  agriculture,  the  initial  cost  of  which  is  often 
larger  than  that  of  humid  agriculture,  to  foster  crops  that 
may  be  manufactured.  Not  only  do  such  crops  make  it 
possible  to  maintain  more  easily  the  fertility  of  the  soil,  but 
they  represent  steady  prices  and  ready  markets. 

174.  Sugar  beets. — The  most  typical  irrigated  crop, 
in  view  of  the  development  of  irrigated  commonwealths, 
is  the  sugar  beet.  All  fairly  fertile  soils  may  produce 
sugar  beets,  providing  proper  methods  of  culture  and 
irrigation  are  followed.  Sugar  beets  endure  alkali 
better  than  most  crops;  they  yield  fairly  well  even  on 
the  shallow,  sandy  or  gravelly  soils  of  the  mesas.  A  clay 
loam  of  good  depth  is  preferable,  if  it  can  be  obtained. 
Sugar  beets  respond  well  to  an  arid  climate  and  to  dry 
summers. 

Sugar  beets  require  careful  soil  preparation  and  an 
even  sowing  and  thinning.  It  is  a  common  practice, 
apparently  to  assure  uniform  and  rapid  germination,  to 
roll  the  soil  after  the  seed  has  been  placed  in  the  ground. 

(286) 


288 


IRRIGATION  PRACTICE 


Rolling  of  the  top  soil,  however,  invariably  causes  a  loss 
of  soil  moisture,  and  it  may  be  necessary  for  the  beet- 
growing  sections  to  revise  their  practice  in  this  particular. 
If  the  soil  is  rolled,  it  should  be  followed  immediately,  if 
possible,  with  a  harrow  to  stir  the  top  soil.  Sugar  beets 
are  always  planted  in  rows,  to  permit  of  easy  cultivation 


FIG.  75.  Unloading  sugar  beets  in  factory  bins. 


between  the  rows,  which  is  usually  done  by  horse  power. 
Cultivation,  an  essential  factor  in  sugar-beet-growing 
under  irrigation,  should  be  practised  after  each  irrigation 
and  two  to  four  times  between  successive  irrigations.  As 
with  other  inter-tilled  crops,  the  more  frequent  and 
thorough  the  cultivation  of  the  soil,  the  smaller  the  quan- 
tity of  water  required  for  the  production  of  the  crop,  and 
the  better  the  quality  of  the  crop. 


SUGAR  BEETS,  POTATOES,  ETC  289 

175.  Method  of  irrigating  sugar  beets. — The  careful 
leveling  of  the  land  before  sowing  adapts  sugar  beet 
fields  to  the  furrow  method  of  irrigation,  although  either 
furrowing  or  flooding  may  be  practised.  In  earlier  days, 
the  field  ditch  method  of  flooding  was  used  for  sugar  beet 
fields,  and  in  California,  today,  many  of  the  beet  fields  are 
irrigated  by  the  border  method  of  flooding.  By  the  flood- 
ing method,  serious  injury  often  results  from  contact 
between  the  water  and  the  heavy  leaves  of  the  beets. 
Especially  on  hot  days,  immediately  after  an  irrigation,  is 
a  kind  of  sun-scald  induced  by  too  much  water  on  the 
ground  near  the  leaves.  Once  a  crop  is  set  back  by  such 
sun-scald,  it  recovers  slowly.  This  trouble  is  largely 
obviated  when  the  furrow  method  is  employed.  All  hi 
all,  the  furrow  method  of  irrigation  gives  the  most  satis- 
factory results  in  sugar  beet  culture  and  is  rapidly  dis- 
placing the  flooding  method.  The  rows  are  usually  about 
3  feet  apart,  with  the  furrows  half  way  between.  If  the 
soil  sub-irrigates  easily,  the  furrow  may  come  between 
every  other  row.  Cross  ditches  are  run  at  the  head  of  the 
field  and  every  300  to  500  feet  to  intercept  the  water  from 
above  and  to  supply  the  adjoining  lower  section  of  the 
field.  The  quantity  of  water  allowed  to  run  down  each 
furrow  is  small,  except  when  a  high  head  is  used  for  the 
special  purpose  of  covering  the  field  quickly.  As  with 
corn  and  the  other  crops  already  discussed,  it  is  well  hot 
to  make  the  rows  too  long.  The  ideal  of  every  method  of 
irrigation  is  to  distribute  the  water  equally  over  the  whole 
field,  so  that  each  plant  may  receive  the  same  quantity  of 
water.  This  is  best  accomplished  by  the  furrow  method 
of  irrigation. 

One  of  the  main  difficulties  in  all  furrow  irrigation  is 
to  secure  a  uniform  application  of  water  in  the  different 
s 


290  IRRIGATION  PRACTICE 

furrows.  Many  soils  "wash"  easily,  and  if  connections 
are  made  with  the  main  supply  ditch  by  simply  hoeing  out 
a  small  opening,  the  water  is  likely  to  make  the  opening 
larger,  or  by  shifting,  even  to  close  it,  so  that  the  water 
does  not  for  any  length  of  time  flow  down  the  furrows  as 
intended  by  the  irrigator.  In  many  sugar  beet  fields  and 
orchards,  small  boxes,  made  of  lath  or  lath-like  boards, 
about  an  inch  square  on  the  ends  and  24  to  30  inches  long, 
are  placed  at  the  head  of  each  furrow-opening,  connecting 
the  furrow  with  the  head  supply  ditch,  and  establishing  a 
permanent  opening  into  each  furrow,  not  easily  disturbed 
by  the  moving  water.  These  boxes  can  be  placed  a  little 
higher  or  lower  with  very  little  effort,  so  that  practically 
the  same  quantity  of  water  may  enter  each  furrow.  With 
devices  of  this  kind  it  is  possible  for  one  man  to  irrigate 
a  very  large  tract  in  a  very  short  time. 

Roeding  determined  the  relative  yields  obtained  when 
the  same  quantity  of  water  was  applied  to  a  sugar  beet 
field  by  the  open  furrow  and  by  the  lath-box  furrow.  When 
lath  boxes  were  used  to  carry  the  water  into  the  furrows, 
thus  providing  a  slower  and  more  regulated  flow,  16.47 
tons  of  beets  were  produced  to  the  acre.  When  the  furrow 
opened  directly  through  the  earth  into  the  supply  ditch, 
making  it  difficult  to  control  the  quantity  and  even  dis- 
tribution of  water,  the  yield  of  beets  per  acre  fell  to  13.72 
tons.  This  emphasizes  the  value  of  an  even  distribution 
of  water  over  the  sugar  beet  field,  and  naturally  over 
fields  of  any  other  crop.  The  sub-irrigation  of  sugar  beets 
has  been  found  feasible  only  in  a  few  localities  where  the 
lands  are  naturally  sub-irrigated.  It  has  not  been  found 
profitable  to  install  subterranean  channels  for  water,  with 
outlets  at  various  intervals,  for  irrigation  purposes. 

176.  Time  to  irrigate  sugar  beets. — The  beet  crop  is 


SUGAR  BEETS,  POTATOES,  ETC.  291 

greatly  benefited  by  winter  irrigation.  The  land  is  bare 
in  fall  .and  winter  so  that  irrigation  cannot  injure  the 
crop,  and  the  soil  is  invariably  benefited  by  late  irriga- 
tions, providing  the  natural  rainfall  of  fall,  winter  and 
spring  is  not  sufficient  to  saturate  the  soil  to  the  full 
depth  of  root-action.  Where  the  winters  are  dry, 
winter  irrigation  of  sugar  beets  has  been  found  very 
profitable. 

There  should  be  water  enough  hi  the  soil  in  the  spring 
to  germinate  the  plants  without  further  irrigation.  If,  at 
the  time  of  seeding,  there  is  not  sufficient  water  in  the 
soil  to  insure  rapid  and  complete  germination,  it  becomes 
necessary  to  apply  water  just  before  or  after  seeding. 
Whether  such  irrigation  for  germination  should  be  before 
or  after  seeding  is  still  undecided.  In  some  sections  the 
general  practice  is  to  irrigate  before  seeding;  in  other 
sections,  excellent  results  are  obtained  by  irrigations 
after  seeding. 

The  first  irrigation  should  be  postponed  as  long  as 
possible  after  planting,  as  early  irrigations  bring  the 
root-system  to  the  surface  and  produce  a  turnip-shaped 
beet  with  a  heavy  growth  of  leaves,  which  hi  turn  means  a 
large,  wasteful  use  of  water  later  in  the  season.  The  sugar 
beet  makes  its  most  rapid  growth  after  late  spring  and 
early  summer,  so  that  the  crop  has  little  need  of  water 
early  hi  the  season.  Evaporation  is  great  from  the  large 
leaf  surface,  and  the  leaves  occasionally  wilt  slightly 
toward  the  end  of  a  hot  day.  This  may  occur  on  soils  well 
supplied  with  water,  and  implies  only  that  water  cannot 
be  drawn  from  the  soil  as  rapidly  as  it  is  evaporated  from 
the  leaves.  If,  in  the  morning,  there  is  no  evidence  of 
wilting,  no  fear  need  be  had  about  the  condition  of  the 
crop,  and  the  next  irrigation  need  not  be  hurried  along; 


292  IRRIGATION  PRACTICE 

but,  if  the  beets  are  wilted  in  the  morning,  it  is  a  fairly 
sure  sign  that  irrigation  is  necessary. 

On  the  deep,  fertile  soils  of  the  West  two  to  four  irri- 
gations should  be  sufficient  for  the  season.  On  porous, 
gravelly  soils,  more  water  will  be  necessary.  Many  of  the 
sugar  factories  advise  two  irrigations;  few  advise  more 
than  three.  In  liberal  practice,  three  to  five  irrigations 
should  be  ample.  The  final  irrigation  should  occur  at 
least  four  to  six  weeks  before  harvest;  that  is,  from  Sep- 
tember 1  to  September  15,  so  that  the  beets  may  have 
ample  time  to  ripen  in  the  cool  weather  of  fall,  and  be 
ready  for  the  factory.  Water  applied  late  causes  late 
growth,  with  a  decided  fall  in  the  sugar  content,  and  often 
in  the  yield.  The  great  length  of  the  growing  season  makes 
it  probably  better  to  apply  a  small  total  quantity  of  water 
in  several  irrigations  than  in  one.  Many  irrigations  tend 
to  give  an  increase  in  the  yield;  but  more  than  four  or 
five  seldom  pay  in  added  yield  for  the  increased  cost  of 
irrigation.  Where  the  annual  rainfall  is  from  12  to  15 
inches,  most  of  which  falls  in  winter  and  early  spring, 
there  is  little  or  no  need  of  irrigation  in  June.  In  July,  when 
the  growth  is  rapid,  two  irrigations;  in  August,  not  more 
than  two,  and  in  September,  at  the  most  one  irrigation 
should  be  applied.  The  Utah  work  indicates  that,  of  the 
total  quantity  of  water  to  be  applied  throughout  a  sea- 
son, about  45  per  cent  should  be  added  in  July;  35  per 
cent  in  August,  and  about  20  per  cent  in  June  and  Sep- 
tember. A  small  total  quantity  during  the  season  elimi- 
nates irrigations  in  June  and  September.  Clay  loams 
should  not  be  irrigated  oftener  than  every  two  weeks.  The 
number  of  irrigations  in  a  season  depends,  after  all,  upon 
the  total  quantity  to  be  used.  With  a  heavy  annual  rain- 
fall, little  irrigation,  therefore  few  applications;  with  light 


SUGAR  BEETS,  POTATOES,  ETC.  293 

rainfall,  more  irrigation  and  more  frequent  applications. 
Beets,  like  all  long-season  crops,  require  water  during 
the  hot  months  of  rapid  growth,  when  the  water  runs  low. 
Under  reservoir  conditions,  this  makes  little  difference, 
since  water  can  be  sent  to  the  farms  at  the  time  of  great- 
est need;  but,  where  canals  are  taken  directly  from  the 
rivers,  it  is  often  difficult  to  supply  a  large  acreage  of  long- 
season  crops  with  all  the  water  needed  in  July  and  August. 


FIG.  76.  Irrigating  potatoes. 

177.  Quantity  of  water  for  beets. — Whether  2>£,  5  or 
7J/2  inches  of  water  are  to  be  applied  at  each  irrigation, 
depends  on  climatic,  soil  and  cultural  conditions.  The 
plant  should  be  allowed  to  drain  thoroughly  the  water 
from  the  soil.  Then,  a  quantity  of  water  should  be  added  to 
bring  the  soil  moisture  up  to  the  full  field  capacity. 
Ordinarily,  4  to  6  inches  are  used  at  each  irrigation,  but 
in  the  hot  summer  months  of  low  water,  2  to  3  inches  only 
are  applied.  It  is  inadvisable  at  any  time  to  apply  in 
one  irrigation  very  large  quantities,  as  for  instance,  1  foot. 


294 


IRRIGATION  PRACTICE 


The  sugar  beet,  like  the  other  crops  hitherto  studied, 
is  subject  to  the  law  that  the  increased  yield  due  to  the 
increase  of  irrigation  is  not  proportional  to  the  added 
quantity  of  water.  Roeding  found,  as  shown  in  the  fol- 
lowing table,  that  during  the  season  of  1905-06,  on  a 
clayey  loam  of  good  depth,  as  the  water  was  increased 
from  6  to  18  inches,  or  three-fold,  the  yield  increased  only 
from  approximately  ten  tons  to  nearly  thirteen  tons  to 
the  acre.  The  Utah  results,  as  also  shown  hi  the  following 
table,  are  practically  the  same. 

YIELDS  OF  SUGAR  BEETS  WITH  VARYING  QUANTITIES  OF 
IRRIGATION  WATER 


Inches  of  irrigation 
water  applied 

Tons  per  acre 

Tons  per  inch 
of  water 

Roeding'  s  results  — 

6.1 

9.7 

1.59 

10.0 

10.8 

1.08 

16.8 

11.8 

0.70 

18.4 

12.8 

0.70 

Utah  results  — 

5.0 

13.8 

2.76 

10.0 

18.6 

1.86 

15.0 

19.5 

1.30 

20.0 

21.3 

1.06 

30.0 

20.8 

0.69 

50.0 

24.5 

0.49 

Water  was  applied  from  5  inches  to  50  inches,  or  ten- 
fold. The  yield  under  this  treatment  increased  from  13.8 
tons  to  24.5  tons,  or  not  quite  double.  Within  these 
limits  the  yield  per  inch  of  irrigation  water  fell  from  2.76 
to  0.49  tons  of  sugar  beets.  (Fig.  77.) 

By  understanding  this  law,  the  possibility  of  30  acre- 
inches  may  well  be  illustrated.  If  30  acre-inches  are  made 
to  cover  1  acre,  the  yield  is  20.82  tons  of  sugar  beets;  2 


SUGAR  BEETS,  POTATOES,  ETC. 


295 


acres,  38.90  tons;  3  acres,  55.89  tons;  4  acres,  64.89  tons; 
6  acres,  82.68  tons.  Whether,  in  consideration  of  the 
scarcity  of  water  and  the  abundance  of  land,  it  would  be 
preferable  to  grow  twenty-one  tons  of  sugar  beets  on  1 
acre  with  30  inches,  or  eighty-three  tons  on  6  acres,  with 
the  same  quantity  of  water,  is  a  thing  that  each  community 
must  determine  for  itself.  However,  it  is  questionable  if 
sugar  beets  should  receive  during  any  season  more  than 
18  inches  of  water,  representing  three  heavy  irrigations, 


\\\\\\\ 


i 


FIG.  77.  Yield  vs.  water  (sugar  beets? 


296  IRRIGATION  PRACTICE 

or  four  lighter  irrigations,  or  six  light  irrigations.  Within 
existing  practice,  sugar  beets  receive  from  15  to  24  inches 
of  water,  according  to  the  prevailing  water  conditions, 
except  in  the  newer  districts  where  water  is  abundant, 
when  even  more  is  used.  The  development  of  more  rational 
methods  will  reduce  the  quantity  now  used. 

The  irrigation  season  for  sugar  beets  seldom  exceeds 
ninety  days.  If  a  depth  of  15  niches  of  water  is  applied 
during  this  season,  a  second-foot  of  water  will  have  a 
duty  of  144  acres;  if  18  inches  are  applied,  a  duty  of  120 
acres,  and  if  24  inches  are  applied,  a  duty  of  90  acres. 
The  present  practice  makes  the  duty  of  water  for  sugar 
beets  about  150  acres,  with  a  rapid  upward  tendency. 

As  explained  in  Chapter  XI,  the  percentages  of  sucrose 
and  purity  are  highest  when  medium  quantities  of  water 
are  used  in  sugar  beet  production.  The  quality  of  sugar 
beets  is  especially  improved  when  water  is  withheld 
several  weeks  before  harvest.  The  ripening  and  increase 
in  sugar  and  purity  go  on  until  very  late  in  the  fall.  Water 
is  often  applied  late,  in  the  hope  that  the  yield  may  be 
increased.  This  seldom  occurs,  and  when  an  increased 
yield  is  obtained,  it  seldom  pays  for  the  labor  of  irriga- 
tion; moreover,  it  causes  a  decided  loss  to  the  sugar  fac- 
tory, which  depends  upon  the  sugar  content  for  its  profit- 
able operation.  Sugar  beets  bought  on  the  basis  of  sugar 
are  not  subjected  to  late  irrigations. 

The  shape  of  the  sugar  beet  is  materially  improved 
when  moderate  quantities  of  water  are  used.  An  early 
irrigation  produces  turnip-shaped  beets,  and  late  or  heavy 
irrigations  produce  forked  or  irregular  beets. 

178.  Carrots. — Carrots  are  grown  practically  as  are 
sugar  beets,  though  less  attention  is  given  to  quality  and 
more  to  the  total  acre  yield.  Irrigation  studies  of  this 


SUGAR  BEETS,  POTATOES,  ETC. 


297 


crop  show  that  carrots  are  subject  to  the  laws  that  prevail 
with  other  crops.  As  shown  in  the  following  table,  when 
the  water  applied  increased  from  3J4  inches  to  60  inches, 
the  total  yield  increased  only  from  7.3  tons  to  34.2  tons 
per  acre;  the  yield  per  inch  of  irrigation  water  diminished 
from  4.35  tons  to  0.57.  However,  carrots  seemed  to 
respond  more  readily  than  did  sugar  beets  to  large  quan- 
tities of  water.  The  total  quantity  of  water  to  be  used 
throughout  the  season  is  about  the  same  as  that  recom- 
mended for  sugar  beets. 

TOTAL  YIELD  OF  CARROTS  WITH  VARYING  QUANTITIES  OF 
IRRIGATION  WATER 


Inches  of  irrigation 
water  applied 

Total  yield  in  tons 

Total  yield 
per  inch  of  water 

3.75 

17.3 

4.35 

7.50 

16.6 

2.22 

15.00 

24.8 

1.65 

25.00 

23.4 

0.94 

35.00 

28.5 

0.82 

60.00 

34.2 

0.57 

179.  Other  root  crops. — Root  crops  are  becoming  of 
greater  importance  as  the  live-stock  business  increases. 
Turnips,  beets,  mangels,  parsnips,  radishes  and  all  similar 
crops,  when  grown  as  field  crops,  may  be  treated  practi- 
cally as  sugar  beets  and  carrots.  When  grown  in  gardens 
they  are  sown  more  closely,  and  the  water  requirements 
are  somewhat  higher.  They  are  always  irrigated  in  fur- 
rows and  precautions  are  taken  not  to  bring  water  in  actual 
contact  with  the  growing  plant,  especially  during  hot 
weather.  Beets  are  usually  irrigated  every  two  weeks; 
radishes  and  early  spring  crops  require  little  total  water, 
but  most  of  it  very  early;  turnips  get  along  with  little 


298 


IRRIGATION  PRACTICE 


water — considerably  less  than  sugar  beets.  Little  exact 
knowledge  has  been  gained  concerning  the  irrigation  of 
these  crops.  Practical  experience,  however,  teaches  that 
much  water  delays  the  time  of  ripening;  it  is  usually 
sufficient  to  irrigate  the  garden  every  two  or  three  weeks; 
water  should  be  taken  off  as  soon  as  ripening  should  com- 
mence; it  is  always  dangerous  to  maintain  water  on  these 
crops  in  the  fall;  and  the  total  water  required  is  not 
greatly  different  from  that  required  for  sugar  beets. 


Fio.  78.  Plan  of  potato  irrigation. 

180.  Potatoes. — Potatoes  are  one  of  the  important 
irrigated  crops.  In  its  water  requirements  the  potato  is 
much  like  the  sugar  beet.  It  is  a  long-season  crop,  requir- 
ing thorough  cultivation.  It  is  deep-rooted  and  prefers 
deep  soil,  and  does  best  on  land  previously  grown  to 
alfalfa. 

Potatoes  should  be  irrigated  by  the  furrow  method, 
although  both  furrowing  and  flooding  methods  are  used. 
Water  is  usually  allowed  to  run  down  between  all  the 


SUGAR  BEETS,  POTATOES,  ETC. 


299 


rows,  although  on  soils  with  good  lateral  seepage  it  may  be 
sufficient  to  irrigate  every  other  row.  Occasionally,  every 
other  row  only  is  irrigated  at  the  first  irrigation,  and  every 
row  thereafter.  (Figs.  76-79.) 

Potatoes  need  a  good  supply  of  water  in  the  soil  at 
planting  time.  If  the  soil  is  too  dry,  it  may  be  necessary 
to  irrigate  the  crop,  which  may  be  accomplished  by 


FIG.  79.  Irrigating  potatoes  at  Greeley,  Colo. 

applying  water  just  before  or  after  planting.  Little  water 
is  needed  by  potatoes  during  the  first  period  of  growth, 
providing  there  is  a  plentiful  supply  in  the  soil  at  the  time 
of  planting.  Potatoes  planted  about  the  first  of  May 
seldom  need  irrigation  before  July  1;  and  from  then  on 
irrigation  should  be  practised  only  as  the  plants  need  it. 
One  of  the  surest  signs  of  water  need  is  the  darkening  of 
the  foliage.  If  water,  especially  cold  water,  is  applied  too 


300 


IRRIGATION  PRACTICE 


frequently,  growth  is  seriously  retarded.  It  is  well  to 
secure  a  good  growth  early,  and  to  develop  early  a  deep 
root-system  that  may  endure  the  heat  of  midsummer.  It 
is  seldom  advisable  to  irrigate  oftener  than  every  two 
weeks,  and  every  three  or  four  weeks  frequently  gives 
satisfactory  results.  Irrigation  should  cease  about  the 
middle  of  August,  leaving  about  sixty  days  for  the  ripen- 
ing of  the  potatoes.  Potatoes  are  seriously  injured  by 
over-irrigation.  The  first  visible  effect  of  too  much  water 
is  a  light  green  color  acquired  by  the  leaves.  The  Utah 
Station  conducted  experiments  on  the  effect  of  varying 
quantities  of  water  on  the  yield  of  potatoes.  Some  of  the 
results  obtained  are  found  in  the  following  table: 


Inches  of 

Yield  in 

Bushels 

Percentage  of 

irrigation  water 
applied 

bushels 
per  acre 

per  inch  of 
irrigation  water 

marketable 
potatoes 

5.0 

154 

30.8                         74.80 

7.5 

182 

24.3 

74.70 

10.0 

195 

19.5 

77.94 

15.0 

227 

15.1 

82.12 

20.0 

267 

13.4 

80.62 

30.0 

244 

8.1 

79.81 

45.0 

253 

5.6 

79.50 

60.0 

304 

5.1 

76.90 

The  total  quantity  of  water  used  varied  from  5  to  60 
inches,  or  twelvefold.  The  yield  of  potatoes  increased 
meanwhile  from  154  bushels  to  304  bushels,  or  not  quite 
double.  The  yield  to  the  inch  of  irrigation  water  fell,  as  the 
water  was  increased,  from  30.8  bushels  to  5.1  bushels  or 
about  one-sixth.  As  shown  in  the  last  column  of  the  above 
table,  the  percentage  of  marketable  potatoes  in  the  total 
crop  increased,  with  the  increase  in  water,  up  to  medium 
quantities,  after  which  it  fell  definitely.  Clearly,  the  laW 


SUGAR  BEETS,  POTATOES,  ETC.  301 

connecting  yield  with  irrigation  is  the  same  for  potatoes 
as  for  other  crops.  However,  the  yield  of  potatoes  is 
more  nearly  proportional  to  the  water  used  than  are 
sugar  beets  or  the  other  root  crops.  This  may  be  due  to 
the  fact  that  the  potato  is  an  enlarged  stem.  Following 
the  Utah  results,  when  30  acre-inches  were  applied  to  1 
acre,  195  bushels  of  potatoes  were  obtained;  when  spread 
over  6  acres,  691  bushels  were  obtained.  (Fig.  84.) 

The  quality  of  potatoes  is  also  definitely  affected  by 
the  quantity  of  water  used.  Medium  quantities  produce 
starchy  potatoes;  if  too  little  or  too  much  water  is  used, 
the  percentage  of  starch  is  materially  lowered. 

It  is  probable  that  the  duty  of  water  for  potatoes 
should  not  be  greatly  different  from  that  for  sugar  beets. 
From  15  to  24  inches  should  represent  an  ample  quantity 
of  water  for  the  production  of  a  good  crop  of  potatoes, 
wherever  the  annual  rainfall  is  hi  the  neighborhood  of  15 
inches,  and  where  the  soils  are  deep  and  well  cultivated. 
It  has  been  found  possible  in  the  arid  regions  to  raise 
large  crops  of  first-class  potatoes  without  irrigation,  and  it 
is  probable  that  the  duty  of  water  for  potatoes  will  be 
greatly  increased  as  fuller  knowledge  is  obtained. 

181.  Peas  and  beans. — Peas  and  beans  are  becoming 
important  irrigated  crops.  They  are  especially  valuable 
because,  like  lucern,  they  grow  well  on  raw  soils  that 
are  unwilling  to  yield  the  ordinary  crops  when  first  brought 
under  cultivation.  Of  late  years  these  crops  have  become 
valuable  hi  the  hog  and  sheep  industry.  The  sheep  eat 
the  vines  and  the  hogs  the  seeds.  Large  quantities  of  the 
proper  varieties  of  peas  are  also  canned,  and  in  that  con- 
dition shipped  all  over  the  earth. 

Peas  and  beans  may  be  grown  either  as  garden  or 
field  crops.  They  are  characterized  by  a  rather  short 


302 


IRRIGATION  PRACTICE 


growing  season,  and  in  that  particular  are  comparable 
with  the  small  grains  and  the  grasses.  They  should  be 
sown  in  rows,  between  which  cultivation  should  be  prac- 
tised as  long  as  possible.  Large  yields  may  be  obtained 
with  small  quantities  of  water,  providing  they  are  care- 
fully cultivated  after  each  irrigation,  and  several  times 
between  successive  irrigations. 


FIG.  80.  Irrigated  "field  peaa 

The  furrow  method  of  irrigation  is  almost  invariably 
used.  The  furrows  are  about  3  feet  apart,  and,  to  avoid 
sun-scald,  so  filled  that  water  does  not  touch  the  plants. 

These  crops  should  be  planted  in  moist  soils,  and,  if 
the  soil  is  dry,  it  may  be  necessary  to  irrigate  them 
either  by  adding  water  just  before  or  after  seeding.  After 
seeding  they  need  little  water  until  the  soil  becomes  some- 
what dry.  However,  they  are  rapid  growers  and  water 


SUGAR  BEETS,  POTATOES,  ETC. 


303 


must  be  applied  whenever  needed,  so  that  they  may 
suffer  no  set-back  because  of  intense  dry  spells.  Peas  and 
beans  finish  most  of  their  growth  hi  spring  and  early  sum- 
mer, when  there  is  usually  an  abundance  of  water.  Just 
before  and  at  the  time  of  blooming  the  largest  quantity 
of  water  is  required.  When  the  pods  are  pretty  well 
formed  little  water  is  required,  and  soon  afterward 
irrigation  may  be  stopped  altogether.  In  fact,  a  somewhat 
dry  soil,  after  the  pods  are  well  formed,  helps  in  the 
formation  of  the  seed.  Peas,  which  require  less  water 
than  beans,  when  grown  for  seed  require  only  one  irriga- 
tion; when  grown  for  fodder,  two  or  three  irrigations  may 
be  applied.  It  is  often  profitable  to  grow  two  crops  of 
peas.  One  is  harvested  early  in  July  and  the  other  hi 
early  fall. 

The  Wyoming  Station  has  conducted  experiments 
on  the  quantity  of  water  used  by  peas.  Some  of  the 
results  obtained  are  shown  hi  the  folio  whig  table: 


Total  inches  of 
irrigation  water 
applied 

Total  tons  of 
forage 
per  acre 

Total  yield  of 
peas  per  acre. 
Bushels 

Per  cent 
of  peas 
in  forage 

22.92 

4.20 

19.21 

14 

20.09 

2.84 

34.75 

37 

17.73 

1.77 

16.56 

28 

9.13 

1.74 

11.17 

19 

5.02 

1.27 

6.04 

14 

•    • 

0.66 

3.00 

14 

The  quantity  of  water  used  varied  from  none  to 
22.92  inches.  The  acre  yield  of  forage  varied  from  .66 
tons  to  4.20  tons.  The  total  acre  yield  of  peas  varied  from 
three  bushels  to  nineteen  bushels.  The  percentage  of 
peas  hi  the  whole  crop  varied  from  14  to  37.  The  yield 
did  not  increase  so  rapidly  as  the  water  increased.  The 


304 


IRRIGATION  PRACTICE 


percentage  of  seed  increased  with  the  water,  which  is 
distinctly  different  from  the  behavior  of  the  grains,  in 
which  the  proportion  of  seed  decreases  with  an  increase 
in  water.  From  10  to  15  niches  of  water  are  probably 
ample  for  the  production  of  peas  or  beans  under  present 
methods.  This  depth  will  be  decreased  as  irrigation  prac- 
tices are  perfected. 


FlG.  81.  Irrigated  celery. 


SUGAR  BEETS,  POTATOES,  ETC. 


305 


FIG.  82.  Irrigated  pumpkins. 


182.  Fiber  crops. — The  strength  of  irrigation  agricul- 
ture will  increase  as  the  crops  grown  are  related  to  manu- 
facturing industries.  The  fiber  crops  are,  therefore,  impor- 
tant. Hemp  grows  exceedingly  well  under  irrigation;  and, 
from  the  irrigated  crop,  fiber  of  the  highest  quality  has 
been  made.  It  is  always  grown  in  rows  and  irrigated  by 
furrows.  Since  it  attains  great  growth  it  requires  consider- 
able water.  Flax  is  likewise  of  easy  culture  under  irriga- 
tion. It  must  always  be  irrigated  by  furrows,  since  it  is 
subject  to  sun-scald.  It  requires  little  water;  in  fact,  it 
has  been  grown  on  dry-farms  with  great  success.  Cotton 
has  been  grown  under  irrigation  for  more  than  fifty  years, 
and  hi  quantities  sufficient  to  supply  a  cotton-mill,  which 
was  established  at  that  time.  In  more  recent  days  cotton- 
growing  has  been  established  successfully  hi  the  Imperial 
Valley  of  California  and  ffi  southern  Arizona.  It  is  irri- 
T 


306  IRRIGATION  PRACTICE 

gated  by  the  furrow  method.  It  uses  little  water.  The 
soil  should  be  moist  at  planting,  and  the  crop  usually 
receives  but  one  irrigation  after  planting. 

183.  Hops. — Hops  is  another  valuable  crop,  which  is 
grown  to  a  limited  extent  under  irrigation.    In  the  humid 
hop-growing  sections,  supplementary  irrigation  is  a  very 
common  practice.    Hops  are  easily  grown,  and  are  irriga- 
ted by  either  the  furrow  or  the  flooding  method.    Water 
is  applied  every  three  or  four  weeks.    The  heaviest  ift|ga- 
tions  are  given  as  the  buds  appear.   No  irrigation  is  appliecJ 
after  August  15,  when  the  crop  is  about  to  ripen. 

184.  Tomatoes,  cantaloupes,  etc. — These  and  similar 
crops   do   excellently  well   under   irrigation.     Tomatoes, 
especially,  have  become  a  very  important  crop  as  canning 
factories  have  been  established.    The  plants  are  set  out  in 
rows  in  the  usual  way,  and  the  water  is  applied  invariably 
by  the  furrow  method.    If  careful  cultivation  is  applied 
to  the  irrigated  field,  the  tomato  plant  does  not  demand  an 
excessively  large  quantity  of  water.     Too  much  water 
encourages  too  great  a  growth  of  vines,  and  interferes 
with  ripening.   The  first  irrigation  is  postponed  as  long  as 
possible  after  planting,  and,  when  the  irrigation  season 
begins,  three  irrigations  are  usually  sufficient  for  the  sea- 
son.   Heavy  irrigation  at  the  time  of  ripening  tends  to 
increase  the  weight  of  the  crop,  and  farmers  who  supply 
the  canning  factories,  therefore,  apply  at  that  time  large 
quantities  of  water;  so  large,  indeed,  that  growth  is  stopped 
and  the  ripening  fruit  is  well  filled  with  water.    In  other 
places,  at  the  time  of  ripening,  water  is  refused  the  plant 
entirely,  leaving  excellent  fruit,  although  the  total  weight 
is  not  so  great.   During  picking  it  is  a  common  practice  to 
apply  water  largely,  with  the  result  that  the  yield  is 
increased.    The  cultivation  of  tomatoes  throughout  the 


SUGAR  BEETS,  POTATOES,  ETC. 


307 


season  is  really  as  important  as  the  irrigation.  The  total 
quantity  of  water  required  for  tomatoes  is  seldom  in 
excess  of  18  inches.  Occasionally,  good  crops  are  pro- 
duced with  less  water. 

Watermelons,  cantaloupe,  squash,  pumpkin,  eggplant 
and  similar  crops  grow  well  under  irrigated  conditions. 
Of  these  crops  the  cantaloupe  is  especially  important.  The 
watermelon  needs  little  water,  and  practically  none  after 
it  is  half  grown.  Two  or  three  irrigations  in  a  season  seem 
to  be  enough.  Cantaloupes  require  a  little  more  water. 


FIG.  83.  Irrigated  onions  in  Arizona. 


308 


IRRIGATION  PRACTICE 


After  flowering,  and  during  fruiting,  more  water  is  required 
than  before.  Cultivation  is  the  main  consideration  in 
the  culture  of  both  watermelon  and  cantaloupe.  To 
obtain  crops  of  high  quality,  water  should  be  limited  at 
the  time  of  ripening.  Pumpkins  and  squash  should  be 
irrigated  very  much  as  the  watermelon.  No  exact  records 
are  available,  but  the  evidence  points  to  10  to  12  inches 
of  water  as  ample  for  most  of  these  crops. 

185.  Cabbage,  cauliflower,  etc. — These  typical  gar- 
den crops,  sometimes  grown  as  field  crops,  use  fairly 
large  quantities  of  water.  The  Utah  Station  has  made 
some  experiments  as  to  the  effect  of  varying  quantities 
of  water.  Some  of  the  results  are  shown  in  the  following 
table : 

YIELDS  OF  CABBAGE  WITH  VARYING  QUANTITIES  OF  IRRIGATION 

WATER 


Inches  of 
irrigation  water 
applied 

Tons  per  acre 

Tons  per  acre-inch 
of  water 

12.5 

9.2 

.74 

20.0 

9.2 

.46 

25.0 

8.2 

.32 

40.0 

10.2 

.26 

70.0 

11.6 

.17 

As  the  total  quantity  of  water  increased  there  was  a 
relatively  small  increase  in  yield.  In  ordinary  practice 
these  crops  receive  small  irrigations  weekly,  or  somewhat 
larger  irrigations  every  other  week.  The  most  important 
thing  in  their  culture  is  to  keep  the  soil  from  becoming 
too  dry  during  the  growing  period.  However,  no  water 
should  be  added  after  the  heads  are  half  formed  as  it  may 
cause  a  splitting  of  the  heads.  Cauliflower  should  be 
treated  much  the  same  as  cabbage.  Lettuce,  spinach  and 


•§ 

5 
=Q 

•i 

!- 
$: 


I 

L 
L 


SUGAR  BEETS,  POTATOES,  ETC. 


Potatoes 


309 


III!      I 


FIG.  84.  Yield  vs.  water  (potatoes). 


parsley  are  crops  that  feed  near  the  surface  and  require 
rather  small  frequent  irrigations.  The  total  quantity  of 
water  required  by  these  crops  is  small. 

186.  Asparagus  and  celery.  —  These  are  important 
and  valuable  irrigated  crops.  Asparagus  needs  water 
chiefly  during  the  cutting  season,  after  which  watering 


310 


IRRIGATION  PRACTICE 


once  a  month  is  ample.  Celery  is  a  water-loving  crop, 
although  if  sufficient  is  added  to  keep  the  soil  in  a  moist 
condition,  the  yield  is  just  as  well  as  if  excessive  quan- 
tities were  added,  and  the  quality  is  better. 

187.  Onions  and  miscellaneous  crops. — Onions  should 
be  planted  in  a  soil  well  filled  with  moisture.  A  month 
may  then  elapse  before  the  first  irrigation.  This  crop  may 
be  irrigated  either  by  the  furrow  or  the  flooding  method. 
Usually  frequent  small  irrigations  are  better  than  infre- 
quent large  ones.  In  middle  summer,  when  growth  is 
rapid,  it  may  need  much  water.  When  the  tops  fall,  irriga- 
tion should  cease.  Maturity  may  be  hastened  by  with- 
holding water  when  the  crop  is  half  grown.  The  Utah 
Station  has  tested  the  effect  of  varying  quantities  of 
water  on  the  yield  of  onions  as  shown  in  the  following 
table: 

YIELDS   OF   ONIONS  WITH   VARYING   QUANTITIES   OF   IRRIGATION 

WATER 


Inches  of 
irrigation  water 
applied 

Tons  per  acre 

Yields  per  acre-inch 
of  water 

15 

10.8 

.71 

20 

11.0 

.55 

30 

16.2 

.55 

65 

16.2 

.27 

The  law  that  the  yield  does  not  increase  in  proportion 
to  the  water  applied  holds  with  onions  as  with  other  crops. 

Rhubarb  requires  frequent  irrigations  during  cutting 
time.  With  good  wettings  in  midsummer,  the  bud-forma- 
tion for  the  next  year  is  furthered. 

Tobacco,  peanuts  and  a  host  of  other  crops  grown  in 
the  world  may  be  brought  under  successful  cultivation 


SUGAR    BEETS,  POTATOES,  ETC. 


311 


in  the  irrigated  section.  These  and  other  crops  should  be 
grown  under  irrigation  as  under  humid  conditions.  Prac- 
tically all  of  them  may  be  grown  successfully  from  the 
first  by  remembering  a  few  general  principles:  The  soil 
should  contain  much  moisture  at  the  time  of  planting. 
The  crops  should 
always  be  planted  in 
rows.  As  a  general 
rule  it  is  best  to  irri- 
gate in  furrows.  Irriga- 
tion should  be  delayed 
until  the  plant  has 
established  its  root- 
system  well  and  until 
it  really  calls  for  water. 
Irrigation  should  occur 
every  two  or  three 
weeks.  Water  should 
be  applied  liberally  at 
the  time  of  flowering. 
Where  the  rainfall  is 


FIG.  85.  Irrigated  Egyptian  cotton. 


from  12  to  15  inches 
annually,  a  quantity  of 
irrigation  water  for  the  season,  from  15  to  24  inches,  is  more 
than  enough  to  make  sure  of  a  good  yield  for  any  crop. 
More  than  that  is  likely  to  cause  deterioration  of  quality 
and  diminution  in  yield.  Less  than  that  often  produces 
the  best  yield.  The  crops  that  grow  throughout  the  season 
are  watered  more  than  those  which  have  short  growing 
seasons.  Crops  that  are  leafy  require  more  water  than 
those  of  small  leaf  surface.  Crops  planted  closely  together 
use  more  water  than  those  planted  far  apart.  All  hi  all, 
more  depends  ordinarily  upon  the  soil  than  upon  irriga- 


312  IRRIGATION  PRACTICE 

tion  in  making  any  new  crop  successful.  If  the  soil  is  of 
the  right  kind,  and  jrrigation  is  practised  in  moderation, 
more  depends  upon^he  careful',  persistent  cultivation  of 
the  soil  than  upon  the  water- or  the  soil.  The  irrigation 
farmer  needs  to  remember  over  and  over  that  irrigation 
is  simply  the  supplementing  of  the  natural  rainfall,  and 


FIG.  86.  Irrigating  cantaloupes. 

that  any  crop  grown  under  natural  rainfall  may  be  grown 
with  irrigation  providing  soil  and  climatic  conditions  are 
%suitable  for  the  crop. 

REFERENCES 

CLARK,  J.  MAX.    Potato  Culture  near  Greeley,  Colorado.    United 

States  Department  of  Agriculture,  Yearbook  for  1904. 
COIT,  J.  ELIOT,  and  PACKARD,  WALTER  E.  Imperial  Valley  Settlers' 

Crop  Manual.    California  Experiment  Station,  Bulletin  No. 

210  (1911). 
CORBET,  L.  C.   Suggestions  to  Potato  Growers  on  Irrigated  Lands. 

United  States  Department  of  Agriculture,   Bureau  of  Plant 

Industry,  Circular  No.  90  (1912). 
GRUBB,  E    H.    Potato  Culture  on  Irrigated  Farms  of  the  West. 

United  States  Department  of  Agriculture,  Farmers'  Bulletin 

No.  386  (1910). 


SUGAR  BEETS,  POTATOES,  ETC.  313 

GRUBB,  E.  H.,  and  GUILFORD,  W.  S.    The  Potato.    Doubleday, 

Page  &  Co.  (1912). 
MCLAUGHLIN,  W.  W.,  and  MORGAN,  E.  R.    Report  on  Irrigation 

Investigations   during    1905-06.     Utah    Experiment   Station, 

Bulletin  No.  99  (1906). 
No  WELL,  HERBERT  T.    Duty  of  Water  on  Field  Pease.    Wyoming 

Experiment  Station,  Bulletin  No.  72  (1906). 

ROEDIXG,  F.  W.    Irrigation  of  Sugar  Beets.    United  States  Depart- 
ment of  Agriculture,  Farmers'  Bulletin  No.  392  (1910). 
TEELE,  R.  P.    Review  of  Ten  Years  of  Irrigation  Investigations. 

United  States  Department  of  Agriculture,  Office  of  Experiment 

Stations,  Annual  Report  for  1908  (separate). 
TOWXSEXD,  C.  O.    Sugar-Beet  Growing  under  Irrigation.    United 

States  Department  of  Agriculture,  Farmers'  Bulletin  No.  567 

(1914). 
WELCH,    J.    S.     Irrigation   Practice.     Idaho   Experiment  Station, 

Bulletin  No.  78  (1914). 
WICKSON,  E.  J.    Irrigation  in  Field  and  Garden.    United  States 

Department  of  Agriculture,  Farmers'  Bulletin  No.  138  (1901). 
WIDTSOE,  J.  A.,  and  MERRILL,  L.  A.    The  Yields  of  Crops  with 

Different  Quantities  of  Irrigation  Water.    Utah  Experiment 

Station,  Bulletin  No.  117  (1912). 
WIDTSOE,  J.  A.,  and  MERRILL,  L.  A.    Methods  for  Increasing  the 

Producing    Power   of    Irrigation    Water.     Utah   Experiment 

Station,  Bulletin  No.  118  (1912). 


CHAPTER  XVI 
FRUIT  TREES,  OTHER  TREES  AND  SHRUBS 

THE  pioneers  of  irrigation  planted  practically  every 
known  fruit  tree  in  the  early  years  of  their  possession 
of  the  West,  and  demonstrated  that  all  would  grow 
to  maturity  and  bear  excellent  fruit.  Apples,  pears, 
peaches,  quinces,  figs,  dates,  oranges,  lemons,  nuts, 
strawberries  and  all  the  small  fruits,  and  a  host  of  others, 
have  been  shown  to  thrive  under  irrigation.  The  people 
of  the  earth  are  consuming  more  and  more  fruit,  and  a 
greater  demand  is  being  made  for  fruit  of  definite  color, 
quality  and  other  desirable  properties.  The  control  that 
irrigation  makes  possible,  together  with  the  favorable 
climate  and  soil  of  the  arid  region,  enables  the  farmer 
to  produce  fruit  of  the  quality  demanded  by  the  markets. 
Fruit-growing  is  becoming  a  great  irrigation  industry, 
and  as  time  goes  on,  fruit  from  the  irrigated  farms  will  be 
sent  over  the  whole  earth. 

188.  Fruit-growing. — Fruit-growing  differs  in  many 
essentials  from  the  production  of  other  farm  crops.  First, 
there  is  a  high  initial  expense  in  preparing  the  land  and 
in  purchasing  and  planting  the  young  trees.  Then,  only 
after  many  years  of  careful  supervision,  entailing  much 
labor,  is  the  first  crop  obtained.  Finally,  for  many  years, 
the  trees  live  and  yield  harvests,  during  which  the  conse- 
quences of  the  mistakes  made  in  the  beginning  are  made 
evident  to  the  farmer.  Therefore,  from  the  first,  extreme 
care  must  be  used  in  fruit-growing. 

(314) 


TREES  AND  SHRUBS  315 

The  methods  of  planting  and  maintaining  trees  are 
not  essentially  different  in  irrigated  and  humid  districts. 
Irrigation  is  the  one  chief  difference,  and  irrigation  is  not 
the  least  important  in  producing  and  maintaining  orchards 
that  justify  the  great  expenditure  of  means  that  must 
be  made  upon  them.  In  orchards,  moreover,  the  greatest 
irrigation  science  has  been  applied,  and  in  them  the 
highest  duty  of  water  has  been  obtained. 

Orchards  lend  themselves  well  to  thorough  cultiva- 
tion, which  may  be  one  reason  for  the  high  duty  of  water 
in  fruit-farming.  It  is  of  extreme  importance  that  cultiva- 
tion be  practised  as  thoroughly  as  possible  in  orchards. 
The  soil  must  be  stirred  immediately  after  each  irriga- 
tion, and  several  times  between  successive  irrigations. 
Both  in  spring,  fall  and  early  growing  season  should  the 
cultivator  be  at  work  in  the  orchard  if  the  farmer  expects 
the  greatest  profit. 

189.  Method  of  orchard  irrigation. — Orchards  may 
be  irrigated  by  any  of  the  methods  already  discussed.  In 
early  irrigation  days,  the  flooding  method  was  most 
generally  employed  in  orchards,  and  even  today  this 
method  is  extensively  used  in  California  and  some  other 
localities.  When  the  flooding  method  is  used  today, 
earth  ridges  are  formed  half  way  between  the  rows  of  trees, 
making  a  set  of  squares  with  a  tree  in  the  middle  of  each. 
These  are  filled  with  water  as  described  in  Chapter  X. 
The  trees  themselves  are  protected  from  direct  contact 
with  the  water  by  earth  heaped  around  the  trunks.  This 
method  has  the  advantage  that  it  covers  the  whole  sur- 
face of  soil  and  insures  a  uniform  penetration  of  water, 
which  has  a  beneficial  effect  upon  the  soil  and  soil  organ- 
isms. However,  much  work  attends  the  throwing  up  of 
the  ridges  and  the  orchard  is  made  unsightly  and  difficult 


316  IRRIGATION  PRACTICE 

to  cultivate  by  the  ridges.  In  other  places  the  check 
method  of  flooding  is  used.  The  whole  orchard  is  sur- 
rounded by  ridges  or  checks,  and  water  is  allowed  to  flow 
into  the  basin  thus  formed.  This  method  is  now  seldom 
used.  The  only  flooding  method  of  today,  besides  the 
basin  method,  is  the  equivalent  of  the  field  ditch  method, 
whereby  water  taken  from  the  head  ditch  by  smaller 
ditches,  is  led  by  small  ditches,  filled  to  overflowing,  over 
the  whole  orchard. 

The  furrow  method  is  the  commonly  adopted  method 
of  all  orchard  irrigation.  By  this  method  a  permanent 
ditch  is  built  at  the  head  of  the  orchard.  This  may  be  a 
flume  or  pipe  made  of  wood  or  concrete.  At  various  inter- 
vals there  are  openings  in  the  ditch  or  flume  to  lead  the 
water  into  the  orchard;  or  if  a  pipe  has  been  laid  under- 
ground, there  are  standpipes  through  which  the  water 
pours  out.  From  this  head  ditch  the  water  is  led  by  fur- 
rows through  the  orchard.  A  head  ditch  carrying  about 
2  second-feet  is  about  right  for  most  orchard  work. 

In  the  furrow  irrigation  of  orchards  it  is  very  difficult 
to  admit  to  each  furrow  the  same  quantity  of  water.  For 
that  reason  small  lath  boxes,  already  described,  are 
employed  to  connect  the  head  ditch  with  each  furrow. 
Instead  of  the  lath  boxes,  small  permanent  pipes  are 
often  placed  at  the  head  of  the  furrows.  The  length  of 
the  furrows  on  sandy  or  gravelly  soils  should  usually  be 
less  than  500  feet,  and  on  clayey,  heavy  soils,  seldom 
more  than  600  feet.  The  shorter  the  furrow,  within  prac- 
tical limits,  the  more  probable  is  the  equal  distribution 
of  water  at  the  head  and  end  of  the  furrow.  The  grade  of 
furrows  preferred  in  orchard  irrigation  is  a  fall  of  3  to  4 
inches  to  each  100  feet.  If  the  land  is  steeper  than  this, 
the  furrows  must  be  carried  around  the  land  in  a  zigzag 


TREES  AND  SHRUBS  317 

fashion.  This  is  a  very  common  orchard  practice  in  notable 
orchard  districts,  as  for  instance,  the  Hood  River  Valley 
of  Oregon. 

Under  good  systems  of  orcharding,  almonds,  pears, 
peaches,  cherries,  apricots  and  oranges  are  spaced  about 
24  feet  apart;  apples  about  30  feet;  walnuts  about  38 
feet;  and  other  trees  in  like  proportion.  This  wide  spac- 
ing makes  necessary  several  furrows  for  irrigation  between 
the  rows  of  trees,  if  the  soil  is  to  be  saturated  thoroughly. 
Young  trees  have  light  water  requirements,  and  one  fur- 
row, not  too  far  from  the  row  of  trees  is  then  usually 
sufficient.  Older  trees  with  wide-spreading  roots  make  it 
necessary  to  move  the  furrows  farther  away.  As  time  goes 
on,  several  furrows  are  made  between  the  rows  of  trees, 
so  that  the  farmer  is  certain  that  the  roots,  wherever 
they  may  be,  are  given  an  ample  supply  of  water.  How- 
ever, if  the  furrows  are  carried  too  near  the  trees  at  the 
beginning  of  growth,  the  roots  may  strike  upward  and 
remain  near  the  surface.  For  that  reason,  the  furrow  is 
placed  at  some  distance  even  from  the  young  tree,  so 
that  the  roots  will  be  made  to  grow  downward  in  search 
of  the  moisture  soaking  down  from  the  furrow.  By  this 
method  it  is  possible  to  establish  deep  root-systems,  which 
are  of  first  importance  in  producing  trees  that  may  endure 
ooccasional  droughts  and  always  make  the  best  use  of 
the  water  stored  in  the  soil  by  rains  or  irrigation. 

Small  furrows,  carrying  little  water,  are  usually  placed 
about  2^2  feet  apart.  Deeper  ones  carrying  more  water 
are  placed  3  to  4  feet  apart.  Some  orchardists  place  the 
furrows  7  or  8  feet  apart  but  make  them  very  deep,  and 
depend  on  lateral  seepage  to.  moisten  all  the  soil.  On 
average  arid  soils  it  is  possible  that  a  distance  of  7  or 
8  feet  apart  for  deep  furrows  is  really  better  than  the 


318 


IRRIGATION  PRACTICE 


distance  of  3  or 
soils  it  is  safe  to 
clayey  soils;  but 
Shallow  furrows 
late  it  has  been 
deep  furrows  are 


4  feet  more  commonly  used.  On  sandy 
place  the  furrows  farther  apart  than  on 
deep,  widely  spaced  furrows  are  the  best, 
were  formerly  used  extensively,  but  of 
demonstrated,  especially  by  Fortier,  that 
by  far  the  better. 


FIG.  87.  Irrigating  an  apple  orchard. 

When  furrows  are  run  in  one  direction  between  the 
rows  of  trees  it  follows  that  there  is  a  space  in  the  row 
between  the  trees  that  is  left  quite  dry.  For  that  reason 
cross  furrows  are  sometimes  run  between  the  trees  at  right 
angles  to  the  main  furrows  so  that  the  land  may  be  more 
uniformly  wetted.  To  cover  the  whole  orchard  uniformly, 
the  furrows  are  often  zigzagged  across  the  orchard  instead 


TREES  AND  SHRUBS  319 

of  following  the  rows.  While  this  system  does  moisten  the 
land  uniformly,  it  is  complicated  and  involves  consider- 
able expense.  Straight  furrows  running  between  the  rows, 
with  occasional  cross  furrows,  is  the  more-1  satisfactory 
system. 

After  each  irrigation,  the  furrow  is  covered  to  diminish 
evaporation.  The  furrows,  therefore,  are  temporary  and 
must  be  made  before  each  irrigation.  It  is  difficult  to 
control  the  water  thoroughly  even  under  the  furrow 
method  of  irrigation.  Some  water,  of  course,  always 
reaches  the  end  of  the  furrows  and  is  allowed  to  flow  into 
a  cross  ditch  at  the  end  of  the  furrows  which  acts  as  head 
ditch  to  the  furrows  below,  or  this  water  may  be  taken  on 
to  fields  of  lucern  or  other  crops.  (Fig.  87;  also  Figs.  41- 
56.) 

190. — Time  of  orchard  irrigation. — Fall  and  winter 
irrigation  is  very  advantageous  in  the  maintenance  of 
orchards.  In  the  colder  parts  of  the  arid  regions,  where 
the  ground,  during  winter,  is  frozen  and  well  covered  with 
snow,  fall  irrigation  alone  is  practised.  The  wood  of  the 
trees  is  allowed  to  ripen  thoroughly  before  fall  irrigation. 
If  water  is  applied  too  early,  so  that  new  growth  starts, 
the  trees  are  hi  danger  of  winter-killing.  In  the  warmer 
parts  of  the  arid  region,  with  mild,  open  winters,  as  in 
Arizona,  winter  irrigation  is  of  greatest  benefit.  Lands 
that  receive  little  precipitation  in  the  whiter  are  especially 
benefited  by  winter  irrigation.  Districts  in  which  the 
precipitation  comes  largely  hi  the  fall,  whiter  or  early 
spring,  are  not  so  greatly  benefited  by  fall  or  winter 
irrigation.  In  such  places  the  added  water  may  simply 
cause  seepage,  which  is  not  desirable. 

Unless  the  soil  is  dry  in  the  spring,  there  is  no  need  of 
spring  irrigation.  As  a  general  rule,  trees  must  not  be 


320  IRRIGATION  PRACTICE 

irrigated,  or  very  cautiously,  when  they  are  in  bloom;  for 
such  early  irrigation  is  said  to  interfere  with  the  setting 
of  the  fruit.  The  proof  of  this  has  not  yet  been  made.  As 
the  hot  season  advances,  water  is  needed,  but  the  first 
irrigation  should  be  postponed  until  really  needed  by  the 
orchard.  In  Washington,  where  the  season  begins  early  and 
there  is  a  high  annual  rainfall,  the  first  irrigation  comes  in 
late  April  or  early  May,  followed  by  three  or  four  irriga- 
tions, from  twenty  to  thirty  days  apart.  In  the  drier  parts 
of  the  arid  region,  where  spring  comes  later,  the  first  irri- 
gation can  be  postponed  until  June  or  even  July.  In  the 
Hood  River  Valley  of  Oregon,  soils  well  saturated  in  the 
spring  need  no  further  irrigation  until  about  July  15.  In 
Colorado,  water  is  applied  to  an  orchard  from  two  to  five 
times  a  season.  In  Idaho,  where  the  first  irrigation  comes 
about  June  15,  three  irrigations  in  a  season  are  said  to  be 
sufficient.  The  Utah  practice  is  the  same  as  that  of 
Idaho.  As  an  average,  two  to  four  summer  irrigations, 
of  3  to  7  acre-inches  each,  and  one  fall  irrigation  should 
be  sufficient  for  deciduous  fruits.  This  means  that  if  irri- 
gation begins  in  June  there  will  be  one  irrigation  every 
three  or  four  weeks  throughout  the  summer  season. 

Orchard  soils  should  not  be  allowed  to  dry  out  too 
much,  for  an  excessive  dryness  in  early  or  middle  summer 
will  injure  the  tree  for  the  whole  season.  On  the  other 
hand,  over-irrigation  tends  to  decrease  fruit-production 
and  delay  the  ripening  of  the  fruit.  The  farmer,  therefore, 
must  remember  not  to  check  the  growth  of  the  fruit  tree 
by  too  little  irrigation,  nor  to  irrigate  so  heavily  that  the 
formation  of  buds  is  decreased  and  ripening  delayed. 
Fruit  trees  make  little  growth  after  July  15,  when  the 
fruit-buds  for  the  following  year  are  being  made.  Exces- 
sive irrigations  at  this  time,  which  force  continued 


TREES  AND  SHRUBS  321 

growth,  tend  to  retard  the  development  of  fruit-buds  for 
the  ensuing  year.  Fruit-buds  seem  to  develop  more 
rapidly  when  growth  is  slow,  due  perhaps  to  the  fact  that 
rapid  growth  consumes  the  supply  of  stored  food,  which 
is  necessary  in  constructing  wood  or  buds.  It  is  the  general 
opinion  that  young  peach  orchards  should  not  be  watered 
after  August  1,  and  that  apples  or  pears  should  not  ordi- 
narily be  watered  after  August  15.  Withholding  water, 
from  these  dates,  enables  the  trees  to  ripen  their  fruit 
properly,  and  to  produce  fruit  of  high  color  and  fine 
quality.  If  the  soil  is  well  stored  with  moisture  early  in 
August,  the  trees  are  not  likely  to  suffer  if  no  further 
irrigations  are  applied.  A  light  green  color  and  dead 
edges  of  the  leaves  and  the  shriveling  of  the  young  fruit 
are  evidences  that  the  soil  moisture  supply  is  so  low 
that  the  root-hairs  are  drying  up.  No  harm  comes  to 
a  tree  that  has  been  irrigated  well  up  to  the  middle  of 
August,  even  if  the  soil  becomes  very  dry  thereafter, 
although  occasionally,  under  such  conditions,  the  leaves 
become  yellow  and  fall  before  frost  comes.  This,  how- 
ever, does  not  injure  the  tree,  and  need  not  worry  the 
farmer. 

Citrous  trees  are  really  evergreens.  They  make  their 
chief  growth  in  autumn,  when  the  deciduous  tree  rests. 
Citrous  trees  are  always  active.  Transpiration  goes  on 
practically  the  whole  year  and  such  trees  must,  therefore, 
be  provided  with  water  in  summer  and  winter.  This 
increases  the  total  water  requirements  and  also  the 
number  of  tunes  that  irrigation  should  be  applied.  Com- 
mon practice  seems  to  be  that,  whereas  deciduous  fruits 
are  irrigated  three  or  four  tunes  during  the  season,  citrous 
trees  must  be  irrigated  at  intervals  of  about  a  month 
each,  leaving  the  wet  season  to  take  care  of  the  trees 
u 


322  IRRIGATION  PRACTICE 

without  further  irrigation.    Each  irrigation  in  California 
is  in  the  neighborhood  of  3  acre-inches. 

191.  Quantity  of  water  for  orchards. — There  is  little 
exact  data  on  the  right  quantity  of  water  to  use  in  orchard 
irrigation.  Orchards  need  less  water  than  a  vigorous  field 
of  alfalfa.  Pears  can  stand  more  water  than  apples; 
apples  more  than  peaches;  citrus  trees  most;  the  olive 


FIG.  88.  On  the  upper  canal. 

endures  very  little  water.  The  true  water  requirements 
depend  on  many  factors,  such  as  climate,  soil,  and  age 
and  nature  of  crop.  A  tree  may  grow  with  a  very  small 
quantity  of  water  which,  however,  may  be  insufficient  to 
produce  fruit. 

The  actual  duty  of  water  in  orchard  irrigation  varies 
from  60  acres  to  400  acres  for  1  second-foot  of  water. 
Fortier  states  the  well-known  truth  that  where  most 


TREES  AND  SHRUBS  323 

water  is  available,  most  water  is  used.  For  instance,  in 
Wyoming,  in  well-watered  sections,  the  duty  of  water  is 
70  acres  per  second-foot;  in  California,  where  water  is 
scarce,  the  duty  is  400  acres  per  second-foot.  Yet,  in  the 
latter  place  citrus  trees  with  long  growing  periods  are 
largely  grown,  and  the  climate  is  hotter  than  in  Wyoming. 
The  whole  question  of  the  quantity  of  water  needed  for 
orchards  needs  careful  investigation.  It  is  probably  safe 
to  say  that  from  12  to  24  niches  is  an  ample  seasonal 
depth  of  water  for  orchard  crops.  More  than  6  acre- 
inches  is  seldom  needed  in  any  one  month,  even  under  low 
rainfall  and  high  evaporation.  That  means,  for  an  irri- 
gation season  of  two  months,  12  inches,  and  of  three 
months,  the  usual  limit,  18  inches.  The  long-season 
citrus  fruits  seldom  need  more  than  3  acre-niches  of  water 
per  month,  although  according  to  Wickson,  citrus  trees 
require  50  per  cent  more  water  for  each  crop  than  do 
deciduous  trees.  Wickson  declares,  however,  that  20 
acre-inches  are  ordinarily  sufficient,  annually,  for  the 
irrigation  of  citrus  trees,  and  that  10  inches  are  frequently 
sufficient. 

192.  Other  conditions  of  orchard  irrigation. — In  young 
orchards,  and  occasionally  hi  old  orchards,  inter-culture 
is  often  practised.  Corn,  potatoes,  beets,  squash  and 
various  vegetables  or  small  fruits  are  planted  between  the 
rows  of  trees.  Moreover,  to  maintain  the  fertility  of  the 
land,  cover-crops  are  occasionally  planted  between  the 
rows  of  older  trees.  Inter-tillage  in  orchards  invariably 
means  a  higher  water  requirement  than  does  clean  cul- 
ture. The  increase  corresponds  to  the  degree  of  inter- 
culture. 

The  great  danger  in  orchard  irrigation  is  over-irri- 
gation. Only  by  moderate  irrigation  can  the  root-system 


324  IRRIGATION  PRACTICE 

be  so  developed  as  to  take  care  of  the  tree  in  seasons  of 
drought.  If  too  much  water  be  used,  the  rising  ground 
water  will  kill  the  roots  and  thus  the  trees.  Trees  that 
have  been  planted  on  soils  with  a  water  table  near  the 
surface  do  not  send  their  roots  into  the  water  and  are 
not  injured;  but,  when  the  roots  have  gone  deeply  into 
the  soil  and  then  are  immersed  in  the  rising  water,  the 
tree  is  sooner  or  later  killed.  Irrigation  cannot  take  the 
place  of  pruning,  cultivation  and  other  approved  horti- 
cultural practices.  When  these  are  attended  to,  relatively 
small  quantities  of  water  will  produce  large  yields  of 
excellent  fruit.  The  orchardist  must  keep  in  mind,  most 
of  all,  that  if  the  soil  itself  is  deep  it  is  a  splendid  water 
reservoir,  in  which  may  be  stored  large  quantities  of 
water  without  making  connection  with  the  standing 
water. 

There  is  often  a  great  hurry  to  make  the  young  tree 
grow  as  rapidly  as  possible  above  ground,  when,  in  fact, 
the  main  thing  is  to  make  the  young  tree  develop  a  deep, 
vigorous  root  system.  The  young  tree,  during  the  first 
year  or  two,  does  not  really  use  much  water;  and,  if  the 
land  to  be  planted  to  trees  is  irrigated  abundantly  before 
planting,  and  then  thoroughly  cultivated,  there  will  be 
little  need  of  irrigation  during  the  first  year.  The  second 
is  the  critical  year  for  the  orchard.  During  this  year  it 
should  be  irrigated  sparingly,  but  cultivated  well.  If  too 
much  growth  is  then  encouraged,  the  trees  may  easily  be 
winter-killed,  and  if  the  roots  are  given  the  wrong  habit 
of  growth,  the  orchard  may  be  injured  permanently. 
With  each  year  more  water  is  needed,  until  maturity  is 
reached. 

At  the  town  of  Hanksville,  Utah,  the  dam  supplying 
the  irrigation  canal  broke,  and  the  people,  disheartened, 


326  IRRIGATION  PRACTICE 

abandoned  their  homes  and  their  orchards.  Five  years 
later,  every  tree  that  had  grown  along  the  ditch  banks  and 
had,  therefore,  developed  shallow  root-systems,  was  dead. 
Every  tree  that  stood  at  considerable  distance  from  the 
ditch  banks  and  had,  therefore,  been  compelled  to  strike 
its  roots  deeply,  was  in  a  most  excellent  condition  and 
carrying  small  quantities  of  fruit.  These  and  similar 
experiences  demonstrate  the  very  great  importance  of  a 
deep  root-system  in  sections  where  drought  or  the  driest 
year  may  come  at  any  time,  through  climatic  variations 
or  some  accident  like  the  breaking  of  a  dam. 

The  quality  of  irrigated  fruit  is  greatly  affected  by 
irrigation.  Lewis  states  that  irrigation  makes  larger, 
more  elongated,  more  angular,  brighter  and  more  attrac- 
tive fruit.  Moderate  irrigations  reduce  the  windfalls,  and 
produce  fruit  of  high  color,  fine  flavor  and  good  shipping 
quality.  Fruit  raised  by  moderate  irrigations  is  pre- 
ferred for  drying  or  canning.  Walnuts*  slip  more  easily 
from  the  skin  if  water  has  been  applied  in  medium  quan- 
tities. Over-irrigation  is  always  an  injurious  practice  in 
fruit-production. 

193.  Nursery  stock. — Nursery  stock  must  be  grown 
in  soil  kept  as  far  as  may  be  possible  at  a  uniform  degree 
of  moisture.    Nursery  stock  does  not  well  resist  sudden 
shocks  of  any  kind. 

194.  Small  fruits. — The  small  fruits,   such  as  dew- 
berries, raspberries,  currants,  blackberries,  strawberries, 
loganberries  and  gooseberries,  are  grown  readily  under 
irrigation,  and  most  of  them  require  very  little  water. 
Cranberries  also  have  been  known  to  yield  well  under 
irrigation  in  especially  constructed  basins. 

There  should  be  an  abundance  of  water  at  planting, 
and  some  water  should  be  kept  in  the  soil  throughout  the 


TREES  AND  SHRUBS  327 

growing  season.  Little  water  should  be  applied  at  flower- 
ing time  and  much  water  at  fruiting  time.  The  wood 
should  be  allowed  to  ripen  for  the  fall  in  comparatively 
dry  soil.  Ordinarily,  irrigation  should  be  stopped  about 
August  1.  Then,  in  late  October  or  early  November, 
another  irrigation  may  be  given,  to  help  produce  a  better 
crop  the  following  year.  The  small  fruits  should  all  be 
irrigated  in  furrows,  and  the  water  should  not  be  allowed 
to  touch  the  plant.  In  general,  the  principles  that  have 
been  developed  with  regard  to  other  crops  hold  with 
these. 

195.  Grape-vines. — The  grape  cannot  stand  much 
water.  In  fact,  grape-vines  grow  without  irrigation  over 
a  large  part  of  the  arid  regions  where  the  annual  rainfall 
is  10  to  15  inches.  The  excessive  use  of  water  is  the  chief 
cause  of  the  troubles  of  the  vine-growers.  Excessive  irri- 
gation causes  mildew  and  similar  troubles,  and  injures  the 
shipping  qualities  of  the  grapes.  In  California,  water  is 
withheld  from  grape-vines  even  to  the  point  where  the 
leaves  begin  to  fall.  Very  superior  fruit  of  high  sugar 
content  and  excellent  flavor  results.  Irrigation  is  done  by 
furrows.  The  furrows  should  be  run  midway  between 
the  rows;  for,  if  they  are  too  near,  mildew  may  set  in, 
and  the  vines  will  trail  in  the  mud.  In  vineyard  culture, 
the  rule  is  to  water  well  when  watering  and  to  cultivate 
several  times  before  the  next  irrigation.  Coit,  speaking  of 
conditions  in  the  Imperial  Valley,  suggests  that  the  last 
irrigation  should  be  given  at  the  commencement  of  the 
ripening  period,  and  that  irrigation  during  the  last  stages 
of  ripening  is  dangerous.  The  grape-vine  must  be  so 
grown  as  to  have  deep  roots,  which  can  be  done  only  by 
the  consistent  use  of  moderate  quantities  of  irrigation 
water. 


328 


IRRIGATION  PRACTICE 


196.  Plants  for  ornament  and  comfort. — Shade  trees, 
shrubs,  flowers — as  windbreaks,  along  the  streets  or  in 
the  gardens — are  all  grown  easily  under  irrigation.  They 
require,  generally,  the  same  treatment  as  other  crops. 
Such  crops  should  be  watered  regularly.  During  the 


FIG.  90.  An  irrigated  date  palm  orchard  in  Arizona. 

season,  more  water  can  be  given  them  than  crops  grown 
for  commercial  purposes.  Forest  trees  are  seldom  grown 
except  for  ornamental  purposes.  In  a  few  sections  of  the 
country,  where  the  settlements  are  far  from  the  railroad 
and  coal  mines,  trees,  notably  the  poplars,  are  grown  to 
furnish  fuel  for  the  farmers.  Trees  for  this  purpose  are 
grown  along  the  ditch  banks,  and  receive  only  such  water 
as  they  absorb  directly  from  the  water  seeping  through 


TREES  AND  SHRUBS  329 

the  ditch  bank.  When  such  trees  are  grown  in  plantations, 
the  quantity  of  water  applied  and  the  manner  of  appli- 
cation are  practically  as  for  orchards,  except  that  more 
water  may  be  applied,  since  the  main  purpose  is  to  produce 
the  largest  possible  wood  growth. 

Practically  every  tree,  shrub  and  flower  known  to  man, 
which  can  endure  the  soil  and  climatic  conditions  of  the 
irrigated  area,  may  be  grown  under  irrigation.  Irri- 
gation is  nothing  more  than  supplementary  rainfall. 
Wherever  rainfall  is  desirable  for  plants,  irrigation  is 
desirable  also. 

REFERENCES 

COIT,  J.  ELIOT.  Olive  Culture  and  Oil  Manufacture.  Arizona  Experi- 
ment Station,  BuUetin  No.  62  (1909). 

COIT,  J.  ELIOT,  and  PACKARD,  W.  E.  Imperial  Valley  Settlers' 
Crop  Manual.  California  Experiment  Station,  Bulletin  No. 
210  (1911). 

ETCHEVERRY,  B.  A.  Practical  Information  on  Irrigation  for  British 
Columbia  Fruit  Growers.  British  Columbia  Department  of 
Agriculture,  BuUetin  No.  44  (1912). 

FORTIER,  SAMUEL.  Irrigation  of  Orchards.  United  States  Depart- 
ment of  Agriculture,  Farmers'  Bulletin  No.  404  (1910). 

FORTIER,  SAMUEL.  Guide  to  Irrigation  Practice  on  the  Pacific 
Coast.  National  Irrigation  Congress,  Bulletin  No.  4  (1907). 

HERRICK,  R.  S.,  and  BENNETT,  E.  R.  The  Colorado  Raspberry 
Industry.  Colorado  Experiment  Station,  Bulletin  No.  171 
(1910). 

LEWIS,  C.  J.,  KRAUS,  E.  J.,  and  REES,  R.  W.  Orchard  Irrigation 
Studies  in  the  Rogue  River  Valley.  Oregon  Experiment  Sta- 
tion, Bulletin  No.  13  (1912). 

LOXGYEAR,  B.  O.  Strawberry  Growing  in  Colorado.  Colorado 
Experiment  Station,  Bulletin  No.  140  (1909). 

McCLATCHiE,  A.  J.  Winter  Irrigation  of  Deciduous  Orchards. 
Arizona  Experiment  Station,  Bulletin  No.  37  (1901). 

PADDOCK,  WENDELL,  and  W^HIPPLE.  O.  B.  Fruit  Growing  in  Arid 
Regions.  Chapter  XIII.  The  Macmillan  Company  (1910). 


330  IRRIGATION  PRACTICE 

SMITH,  RALPH  E.  Walnut  Culture  in  California.  California  Experi- 
ment Station,  Bulletin  No.  231  (1912). 

WHIFFLE,  O.  B.  Grape  Growing.  Colorado  Experiment  Station, 
Bulletin  No.  141  (1909). 

WICKSON,  E.  J.  Irrigation  in  Fruit  Growing.  United  States  Depart- 
ment of  Agriculture,  Farmers'  Bulletin  No.  116  (1900). 

WICKSON,  E.  J.  Irrigation  among  Fruit  Growers  of  the  Pacific 
Coast.  United  States  Department  of  Agriculture,  Office  of 
Experiment  Stations,  Bulletin  No.  108  (1902). 


CHAPTER  XVII 

THE  DUTY,  MEASUREMENT  AND  DIVISION 
OF  WATER 

IN  the  foregoing  chapters  have  been  elucidated  the 
known  laws  governing  the  relationship  that  exists  between 
soils,  plants  and  water.  Results  obtained  under  well- 
controlled  laboratory  or  experimental  field  conditions  may 
often  differ  from  those  obtained  in  general  field  practice. 
This  chapter,  therefore,  discusses  the  practical  duty  of 
water  and  the  methods  of  measuring  and  distributing 
irrigation  water,  so  that  ideal  conditions  may  be  ap- 
proached. 

197.  The  duty  of  water. — The  duty  of  water,  a  term 
long  since  coined,  means  the  quantity  of  water  needed  to 
mature  crops.  It  may  be  expressed  in  various  ways. 
Sometimes  the  duty  of  water  is  expressed  as  the  number  of 
pounds  of  water  required  to  produce  one  pound  of  the 
dry  matter  of  the  crop;  under  other  conditions,  as  the 
depth  of  water  over  the  field,  required  during  the  growing 
season,  to  produce  the  crop.  More  commonly,  however, 
the  duty  of  water  is  expressed  as  the  number  of  acres 
that  may  be  irrigated  by  a  definite  quantity  of  water, 
say  a  second-foot,  flowing  continuously  throughout  the 
growing  season.  In  Canada,  the  United  States,  India, 
Australia  and  other  irrigated  countries,  this  is  by  far 
the  most  common  method  of  expressing  the  duty  of 
water.  The  reason  for  this  popularity  seems  to  be  that 
irrigation  canals  are  generally  taken  directly  from 

(331) 


332  IRRIGATION  PRACTICE 

streams  having  a  continuous  flow  during  the  irrigation 
season. 

Various  units  for  measuring  water  are  used  in  different 
parts  of  the  country,  such  as  the  miner's  inch,  but  the 
only  one  in  modern  general  use  is  the  cusec  or  second-foot, 
which  means  1  cubic  foot  of  water  passing  a  given  point 


FIG.  91.  Canal  crossing  river  in  an  inverted  syphon. 

each  second  of  time.  The  duty  of  a  given  stream  would 
then  be  the  number  of  acres  irrigated  per  second-foot, 
flowing  continuously  during  the  season.  This  duty  may 
easily  be  converted  into  acre-inches  or  acre-feet  of  water. 
One  second-foot,  flowing  for  twenty-four  hours,  will 
cover  1  acre  to  a  depth  of  nearly  2  feet.  If  the  time  is 
known  during  which  a  second-foot  of  water  has  been 
flowing  over  a  given  area,  it  is  but  a  moment's  calcula- 


DUTY  AND  DIVISION  OF  WATER 


333 


tion  to  determine  the  depth  to  which  the  land  has  been 
covered. 

The  time  during  which  a  given  volume  of  water  flows 
is  of  first  importance  in  determining  the  duty  of  the 
stream.  A  canal  carrying  10  second-feet  of  water  may  be 
filled  from  May  1  to  November  1;  and  during  that  tune 
may  irrigate  1,000  acres  of  land.  The  quantity  of  water 


FIG.  92.  Looking  down  the  Bear  River  Canal. 

passing  through  the  canal  during  the  six  months  in 
question  would  cover  the  1,000  acres  to  a  depth  of  nearly 
39  inches.  In  fact,  however,  the  water  was  used  for  irri- 
gation purposes  only  about  seventy-five  days  out  of  the 
six  months  and  the  actual  depth  of  water  given  the  crop 
was  only  about  18  inches.  The  duty  of  water  expressed 
as  the  area  covered  by  a  given  volume  of  water,  flowing 
continuously,  may,  therefore,  become  very  misleading 


334  IRRIGATION  PRACTICE 

unless  it  is  carefully  specified  that  the  water  was  used 
during  a  certain  number  of  days. 

Canals  taken  directly  out  of  the  river  usually  carry 
water  from  early  spring  until  late  fall,  but  the  water  so 
delivered  before  and  after  the  irrigation  season  should 
not  be  charged  to  the  duty  of  water.  When  the  waters 
are  held  back  in  reservoirs,  water  is  of  course  allowed  to 
flow  through  the  canal  only  during  the  irrigation  season. 

The  relationships  existing  among  the  quantity  of  flow- 
ing water,  the  number  of  acres  to  be  irrigated  and  the 
depth  to  which  the  land  will  be  covered  may  be  shown  in 
simple  formulas: 

A  =  Area  to  be  irrigated. 

D  =  Duty  of  water,  that  is  the  acres  matured  by  1 

second-foot  flowing  continuously  for  a  definite 

period. 
B  =  The  time  in  days  1  second-foot  flows  to  mature 

crop. 
S  =  The  depth  in  inches  of  the  given  volume  of  water 

over  the  area  irrigated. 
F  =  The  discharge  of  second-feet  necessary  to  irrigate 

the  given  area  A,  with  the  duty  D. 
The  following  relationship  may  then  be  established: 

S  =      X  23.8. 


D     BX23.8 

198.  Classes  of  duty.  —  The  theoretical  duty  of  water 
is  never  quite  realized  in  practice.  The  term  "duty  of 
water"  does  not  refer  to  the  theoretical  deductions  in 
laboratory  experiments,  but  refers  invariably  to  the  water- 
cost  of  crops  under  practical  conditions.  It  is,  therefore, 


DUTY  AND  DIVISION  OF  WATER 


335 


a  term  which  cannot,  under  present  conditions,  be  fixed. 
As  time  goes  on,  and  irrigation  practices  are  improved, 
there  will  be  an  increasingly  high  duty  of  water  obtained 
in  the  irrigated  section. 

The  absolute  duty  of  water  means  the  sum  of  the  water 
applied  to  the  plant  in  irrigation  and  the  water  supplied 
from  the  soil  moisture  and  by  rains  during  the  growing 
season.  This  duty  is  usually  expressed  as  the  depth  in 


FIG.  93.   Lateral  outtake  from  large  canal. 


inches  over  the  land.  For  instance,  in  a  certain  experi- 
ment, 6.4  inches  of  water  were  taken  from  the  soil;  15.3 
inches  were  added  by  irrigation,  making  a  total  of  21.7 
inches,  the  absolute  duty. 

The  net  duty  of  water  means  the  area  of  land  covered 
by  the  water  received  by  the  farmer  at  the  farm  head- 
gate.  It  is  practically  identical  with  the  absolute  duty, 
except  that  the  water  stored  in  the  soil  and  the  rains  during 
the  summer  are  not  taken  into  account. 

The  gross  duty  of  water  means  the  area  of  land  served 
by  the  water  at  the  intake  of  the  canal,  or  occasionally 


336  IRRIGATION  PRACTICE 

at  the  intake  of  the  large  lateral.  It  is  the  duty  for  the 
whole  system  and  is  of  primary  interest  to  the  engineers 
who  design  irrigation  systems.  In  transit  from  the  head 
of  the  main  canal  to  the  farm  where  the  water  is  applied 
to  the  crops,  large  volumes  of  water  are  lost  by  evaporation 
and  seepage,  and  the  duty  of  water  for  the  system  does 
not  at  all  represent  the  actual  water  requirement  of  the 
crops  grown  under  the  system.  The  net  duty  is  therefore 
of  prime  value  to  the  farmer  whose  chief  interest  is  in  the 
water  actually  received  by  him  at  his  farm. 

199.  Determination  of  duty  of  water  difficult. — The 
duty  of  water  under  any  irrigation  system  is  always  diffi- 
cult to  determine.  The  soil,  climate,  methods  and  time 
of  application  and  many  other  factors  do  much  to  increase 
or  decrease  the  area  that  may  be  served  by  a  given  quan- 
tity of  water.  The  reservoirs  and  canals  themselves, 
whether  lined  or  unlined,  whether  passing  over  gravelly 
strata  or  clay  beds,  determine  in  large  degree  the  gross 
duty  under  the  system.  After  all  such  factors  have  been 
taken  into  consideration,  there  remains,  as  a  disturbing 
factor,  the  law  that  the  more  water  is  added  to  a  crop,  the 
smaller  the  yield  to  the  unit  of  water.  This  law  of  increas- 
ing water-cost  brings  always  to  the  front  the  question  of 
whether  much  water  shall  be  used  to  obtain  the  largest 
possible  yield  an  acre,  or  whether  moderate  quantities 
shall  be  used  to  obtain  the  largest  yield  from  each  acre- 
foot  of  water.  There  is  a  depth  of  water  for  each  set  of 
land,  crop  and  water  conditions,  which  produces  the 
greatest  profits.  When  water  is  added  above  or  below  this 
point  the  profitableness  decreases.  This  point  of  optimum 
duty  will,  as  our  knowledge  increases,  be  determined  for 
different  crops  and  irrigation  projects. 

An  example  will  illustrate  what  is  meant  by  this  point 


DUTY  AND  DIVISION  OF  WATER 


337 


of  highest  profitableness  or  optimum  duty.  A  beet  field 
is  supplying  beets  to  the  factory  at  a  contract  price  of 
So  a  ton.  The  total  cost  of  producing  the  beets,  includ- 
ing interest  on  the  investment,  may  be  assumed  to  be  $60 
an  acre.  The  following  table  may  then  be  constructed  on 
the  basis  of  the  crop  yields  in  the  Utah  experiments  on 
the  effect  of  varying  quantities  of  water  on  the  growth  of 
crops: 


£  o        -2"oo    j    *s            -  -         -             & 

30  acre- 
inches 
spread 
over 

11        ^ 

I! 

il 

oss  incom 
om  beets 

S 

1 

•s 

'otal  cost 

et  income 
om  beets 

•   —          ^i  ^ 

o  3? 

o 

*^jz 

£°       >3  g.      H-" 

£ 

o"5 

0 

i 

1  acre      .    . 

30.0       21.0        21 

$5 

$105 

$60 

$60        $45 

2  acres     .    . 

15.0       19.5        39            5 

195         60 

120    ;      75 

3  acres     .    . 

10.0       18.6        56            5 

280         60 

180        100 

4  acres    .    . 

7.5       16.3         65            5          325         60 

240 

85 

1 

| 

Under  the  above  conditions,  the  largest  net  income, 
SI 00,  was  obtained  when  30  acre-niches  were  spread  over 
3  acres.  When  spread  over  less  or  more  land  than  this 
the  net  income  decreased.  Similar  results  must  be  deter-* 
mined  for  all  of  the  standard  crops,  so  that  for  any  set  of 
conditions  the  most  profitable  depth  of  water  may  be 
known. 

In  different  sections  of  the  irrigated  regions,  1  second- 
foot  of  water  serves  from  25  to  over  300  acres,  with  an 
average  near  75  to  100  acres.  This  great  variation  is 
partly  due  to  the  differences  in  rainfall.  Wherever  the 
rainfall  is  high,  less  irrigation  water  is  required  to  mature 
crops.  This  is  not  the  main  cause  of  the  varying  duty  of 
water,  for  the  highest  duty  is  usually  found  where  the 
rainfall  is  light,  as  in  southern  California.  Differences 
v 


338  IRRIGATION  PRACTICE 

in  the  duty  of  water  lie  rather  in  the  practices  of  the  farmer, 
who  usually  feels  that  the  more  he  irrigates  his  crops,  the 
greater  will  be  his  reward.  Every  irrigation  farmer  is 
something  of  a  water  hog.  His  safety  lies  in  the  irrigation 
canal,  especially  in  the  lateral  which  leads  to  his  farm. 
One  of  his  main  efforts  is  to  secure  the  largest  possible 
quantity  of  water  for  his  land.  As  a  consequence,  the 
varying  duty  of  water  can  ordinarily  be  correlated  with 
the  quantity  of  water  available  in  various  localities. 
Wherever  water  is  abundant,  the  duty  is  low;  wherever 
limited,  the  duty  is  high.  At  the  upper  end  of  the  canal 
the  duty  is  less  than  at  the  lower  end,  for  the  farmer  at 
the  head  has  the  first  chance  and  uses  all  he  can  get, 
usually  to  the  detriment  of  his  crop. 

200.  Duty  of  water  in  Africa. — Egyptian  irrigation 
antedates  written  history.  The  early  Egyptians  gave 
careful  attention  to  the  development  of  a  permanent 
system  of  irrigation.  The  modern  government  of  Egypt 
has  likewise  given  very  careful  attention  to  irrigation  and 
some  of  the  largest  modern  irrigation  projects  have  been 
constructed  in  Egypt. 

The  climate  of  Egypt  is  very  arid.  According  to  Sir 
William  Willcox,  the  average  annual  rainfall  at  Alexandria 
is  about  9  inches,  at  Cairo  about  1J^  inchee,  and  at 
Assuan  practically  no  rain  falls.  Under  such  a  dry  climate, 
the  water  requirements  of  crops  should  be  very  high, 
and  the  duty  of  water  very  low.  As  reported  by  Willcox, 
during  an  irrigation  season  of  about  seventy-five  days,  1 
second-foot  has  a  duty  for  cotton  and  other  dry  crops  of 
115  acres;  for  rice,  60  acres.  This  is  not  far  from  the  aver- 
age results  obtained  in  other  countries  where  much  more 
rain  falls.  Nevertheless,  the  methods  of  irrigation  prac- 
tised in  Egypt  tend  to  waste  considerable  portions  of 


DUTY  AND  DIVISION  OF  WATER  339 

water,  and  make  it  unlikely  that  the  duty  as  above  given 
represents  the  most  economical  use  of  water.  When  the 
Nile  overflows,  water  is  conducted  into  large  basins  and 
allowed  to  stand  there  until  the  silt  carried  by  the  river 
water  is  deposited  and  the  soil  itself  has  become  thor- 
oughly saturated  with  water.  Afterwards  the  surface 
water  is  allowed  to  flow  back  into  the  Nile.  This  makes  it 
certain  that  plants  do  not  use  all  the  water  actually  applied 
to  the  soil.  Moreover,  the  above  results  represent  the 
gross  duty  of  water  in  Egypt.  Few  studies  have  been 
made  of  the  net  duty,  but  since  the  gross  duty  varies 
little  from  that  obtained  in  other  sections  of  the  world, 
it  is  likely  that  the  net  duty  is  not  greatly  different  from 
that  obtained  in  other  parts  of  the  world. 

Some  investigations  have  been  made  also  on  the  duty 
of  water  hi  southern  Africa.  According  to  Mawson,  the 
duty  of  water  in  South  Africa,  under  an  annual  rainfall 
of  20  to  35  niches,  is,  for  grain,  115  acres;  for  vegetables, 
100  to  180  acres;  for  cereal  crops,  140  to  200  acres;  for 
sugar-cane,  50  to  70  acres;  for  fruit  trees,  200  to  300  acres. 
In  the  Cape  Colony,  the  duty  of  water  has  been  found  to 
vary  from  150  to  285  acres,  although  two  crops  were  raised 
on  the  land.  In  the  Transvaal,  not  quite  24  acre-inches  of 
water  are  applied  to  land  for  the  production  of  crops. 

201.  Duty  of  water  in  Asia. — In  Asia,  as  in  Egypt, 
irrigation  has  been  practised  from  before  written  history. 
The  best  example  of  Asiatic  irrigation  is  India.  More 
systematic  irrigation  work  has  probably  been  done  re- 
cently in  India  than  hi  any  other  part  of  the  world, 
unless  it  be  the  recent  irrigation  progress  hi  western 
United  States  and  western  Canada. 

The  rainfall  of  India  varies  greatly,  from  the  highest 
hi  the  world  to  a  condition  of  extreme  aridity.  Over  the 


340  IRRIGATION  PRACTICE 

Ganges  delta,  the  average  annual  rainfall  varies  from  60 
to  70  inches,  whereas  over  the  Northwest  Provinces  it  is 
in  the  neighborhood  of  25  inches. 

The  duty  of  water  in  India  has  been  investigated  under 
government  supervision,  and  much  has  been  published 


FIG.  94.  Headgate  of  a  canal. 

concerning  it.  R.  B.  Buckley,  the  chief  authority  on 
East  Indian  irrigation,  states  that  the  gross  duty  of  water 
during  the  wet  season — from  June  to  October — varies 
from  about  80  to  170  acres  to  the  second-foot.  During 
the  cold  season — from  November  to  March — the  duty  of 
water  varies  from  about  90  to  200  acres  to  the  second-foot 
of  water.  The  duty  of  water  varies  greatly,  even  under 
the  same  canal,  if  different  sections  are  considered.  In 
India,  as  elsewhere,  it  seems  to  be  true  that  the  more 


DUTY  AND  DIVISION  OF  WATER  341 

water  available,  the  more  used.  Moreover,  varying  seepage 
in  different  localities  causes  a  varying  gross  duty  of  water. 
In  one  exhaustive  study  of  the  duty  of  water,  it  was  found 
that  under  a  given  system,  20  acre-inches  were  actually 
used  for  the  production  of  crops;  while  in  another  place 
four  irrigations  of  2%  acre-inches  each,  or  a  total  of 
10  acre-inches,  produced  abundant  crops  of  wheat. 
Kennedy,  who  carried  on  experiments  under  the  Barri- 
Doab  Canal,  found  that  wheat,  barley,  coffee;  Indian 
corn  and  cotton  required  during  the  season  10.6  inches 
of  water;  and  sugar-cane  25.7  inches.  These  results  show 
that  the  water  requirements  of  crops  in  India  are  practi- 
cally identical  with  those  in  America  and  other  countries 
of  the  world. 

The  loss  of  water  from  the  main  Indian  canals  varies 
from  20  to  75  per  cent  and,  consequently,  the  net  duty  of 
water  in  India  is  much  greater  than  the  gross  duty.  In 
one  series  of  investigations  it  was  found  that  even  the  lat- 
erals from  the  main  canal  served  a  much  larger  area  than 
the  whole  canal,  per  second-foot  of  water,  the  difference 
rising  occasionally  to  30  or  40  per  cent. 

Under  several  of  the  Indian  canals,  160  acres  have 
been  adopted  as  the  duty  of  water  for  1  second-foot  under 
the  whole  system.  This  compares  very  favorably  with 
present  practices  in  the  United  States. 

202.  Duty  of  water  in  Europe. — Irrigation  is  generally 
practised  in  Europe,  especially  in  France,  Spain  and  Italy. 
In  these  latter  countries,  irrigation  goes  back  many 
hundreds  of  years,  and  the  methods  now  followed  are 
based  upon  the  experience  of  centuries.  True,  in  southern 
Europe,  irrigation  is  not  a  matter  of  life  and  death,  as 
in  the  more  arid  sections  of  the  world,  but  it  has  done  and 
is  doing  much  to  increase  the  wealth  and  prosperity  of 


342  IRRIGATION  PRACTICE 

southern  Europe,  for,  without  irrigation,  some  of  the  most 
fertile  sections  of  southern  Europe  would  be  of  mediocre 
producing  power. 

The  duty  of  water  under  European  canals  does  not 
differ  greatly  from  that  observed  under  canals  of  other 
countries.  In  France,  the  duty  has  been  found  to  vary  from 
about  40  to  nearly  200  acres  to  the  second-foot  of  water. 
The  lower  duty  of  water  prevails  where  water  meadows 
are  maintained,  which  are  not  a  true  form  of  irrigation 
agriculture.  Under  the  carefully  managed  canals  of 
France  the  duty  ranges  from  100  to  nearly  200  acres  to  the 
second-foot  of  water.  In  Italy,  the  duty  of  water  varies 
from  about  40  to  100  or  more  acres  per  second-foot,  and 
occasionally  reaches  300  acres  where  Indian  corn  and 
similar  crops  are  raised.  In  Spain,  where  economy  in  the 
use  of  water  has  been  carried  to  a  high  degree,  an  average 
duty,  under  twenty  canals,  was  found  to  be  172  acres  to 
the  second-foot  of  water.  As  an  average  of  one  series  of 
measurements  under  the  chief  canals  of  France,  Italy  and 
Spain,  1  second-foot  of  water  serves  239  acres  of  the  stand- 
ard crops  of  those  countries.  Generally  speaking,  there- 
fore, the  duty  of  water  in  southern  Europe  is  somewhat 
higher  than  in  Egypt,  India  or  the  United  States. 

203.  Duty  of  water  in  South  America. — Few  data 
exist  concerning  the  duty  of  irrigation  water  in  South 
America.  In  prehistoric  times,  large  irrigation  projects 
existed  in  South  America,  the  remains  of  which  give 
testimony  of  the  excellence  of  South  American  irrigation 
in  earlier  days.  In  northern  Peru,  which  is  practically 
rainless,  it  is  reported  that  the  duty  of  water  is  160  acres 
to  the  second-foot  of  water;  and  in  northern  Chili,  which 
is  also  practically  rainless,  the  duty  is  about  190  acres  to 
the  second-foot  of  water.  These  figures  are  averages,  for 


DUTY  AND  DIVISION  OF  WATER  343 

special  districts.    It  is  not  likely  that  any  unusually  high 
duty  of  water  prevails  in  South  America. 

204.  Duty  of  water  in  Australia. — Irrigation  on  a  large 
scale  is  just  beginning  to  be  developed  in  Australia.    The 
methods  there  adopted  are  based  upon  the  best  practices 
of  the  world,  notably  upon  those  of  the  United  States. 
The  duty  of  water,  as  it  is  developed  in  Australia,  does 
not  differ  materially  from  that  of  North  America.   Many 
of  the  projects  are  comparatively  new  and  the  duty  is 
low,  but  will  become  higher  as  more  complete  irrigation 
practices  are  adopted. 

205.  Duty  of  water  in  North  America. — The   chief 
irrigated  section  of  North  America  covers  western  Canada 
and  the  western  United  States.    These  two  districts  are 
so  similar  in  climatic  and  soil  conditions  that  whatever 
is  true  of  one  is  generally  true  of  the  other.  Some  excellent 
duty  of  water  experiments  have  been  made  for  this  section, 
by  the  United  States  Department  of  Agriculture  under 
the  direction  first  of  Elwood  Mead  and  later  of  Samuel 
Fortier.    The  gross   duty  of  water  was  determined  for 
a  number  of  representative  canals  in  all  of  the  western 
states.  As  a  general  result,  Teele  declares  that  "It  appears 
that  3^  to  4  acre-feet  are  required  at  the  heads  of  unlined 
earth  canals.    This  can  be  taken  safely  as  a  basis  for 
computation."    This  means  that  the  duty  of  water  for 
1  second-foot,   flowing  for  60  days,  varies  from  34  to 
27   acres;  flowing  for  120   days,  from   68   to  54   acres, 
and  flowing  for  180  days,  from  102  to  80  acres.   This  gross 
duty  for  western  North  America  does  not  represent,  even 
approximately,  the  net  duty  of  water,  for  the  irrigation 
investigations  of  the  United  States  Department  of  Agri- 
culture have  shown  for  a  series  of  representative  canals 
that  nearly  60  per  cent  of  the  water  is  lost  between  the 


344  IRRIGATION  PRACTICE 

headgate  of  the  canal  and  the  laterals,  and  undoubtedly 
much  of  the  remaining  40  per  cent  is  lost  between  the 
heads  of  the  laterals  and  the  farms.  Observations  were 
also  made  by  the  government  investigators  on  the  quan- 
tities of  water  actually  applied  to  crops,  with  average 
results  as  follows:  Alfalfa,  32  inches;  wheat,  18  inches; 
barley,  16  inches;  potatoes,  28  inches;  sugar  beets,  25 
inches,  with  an  average  for  these  crops  of  about  23  acre- 
inches.  For  an  irrigation  season  of  about  ninety  days, 
this  would  mean  a  net  duty  of  100  acres.  This  is  much 
larger  than  the  gross  duty  as  above  given.  The  losses 
from  the  canals  are  always  large,  averaging  5.77  per  cent 
per  mile;  and  Fortier  declares  that  perhaps  less  than  one- 
third  of  the  water  diverted  by  the  canals  is  actually  used 
by  the  crops. 

206.  Bear  River  Canal  experience. — One  of  the  most 
notable  canals  in  western  America  is  the  Bear  River 
Canal,  which  began  its  actual  operations  in  1891.  Its 
first  duty  of  water  was  40  acres  for  six  months  for  each 
second-foot  of  water,  or  a  depth  of  4.2  feet  during  the 
six  months.  In  1903,  after  twelve  years  of  experience,  it 
was  obvious  that  too  much  water  was  being  used.  The 
ground  water  table  was  rising  rapidly  near  the  surface, 
alkali  was  becoming  visible  in  certain  low  sections,  and, 
all  in  all,  the  evils  from  over-irrigation  were  observed. 
Careful  measurements  were  then  made  of  the  water 
delivered,  and  attempts  were  made  to  increase  the  duty 
of  water.  For  four  years  thereafter,  6,000  measurements 
were  made  at  the  head  of  the  canal,  at  the  heads  of  the 
laterals,  and  at  the  gates  to  the  individual  farms.  Accord- 
ing to  Wheelon,  it  was  found  in  1903  that  a  duty  of  67 
acres  per  second-foot  prevailed.  In  1904,  this  had  been 
raised  to  120  acres,  and  in  1905  to  138  acres.  These 


DUTY  AND  DIVISION  OF  WATER  345 

duties  were  calculated  from  the  measurements  taken  at 
the  heads  of  the  laterals  and  are  smaller  than  would  be 
the  case  were  measurements  made  at  the  farms  them- 
selves. During  these  years  of  increasing  duty,  crop- 
yields  were  equally  good,  and  crop  quality  was  improved. 
The  increasing  duty  of  water  under  this  system  is  still 
going  on,  with  the  result  that  farming  conditions  are 
being  greatly  improved.  This  is  the  history  of  all  the 
larger  canals  in  America  that  have  received  competent 
and  constant  supervision.  The  duty  of  water  is  steadily 
increasing  throughout  the  whole  of  western  America. 

207.  Idaho  results. — A  series  of  recent  investigations 
in  Idaho  further  brings  out  the  present  duty  of  water  in 
wrestern  America.    Bark  measured  the  quantities  of  water 
used  by  168  Idaho  farmers.    Most  of  these  farmers  had 
been  farming  only  a  few  years,  and  since  the  duty  of 
water  is  always  lowest  at  the  beginning  of  irrigation  prac- 
tice,  the  measurements  represent  maximum  use.     The 
irrigation  season  for  grain  varied  from  thirty-six  to  forty- 
six  days,  and  for  alfalfa  from  ninety-six  to  one  hundred 
and  twenty-two  days.    It  was  found  that  the  crops  re- 
ceived on  an  average  practically  2  feet,  or  24  inches  of 
water,  which,  for  an  irrigation  season  of  four  months,  would 
be  equivalent  to  about  120  acres  to  the  second-foot  of  water. 
Where  water  was  plentiful,  much  was  used;  where  water 
was  scarce,  little  was  used.    Moreover,  it  was  found  that 
the  entire  need  for  water  fell  on  the  four  months,  May  to 
August  inclusive.    It  is  likely  that  for  all  ordinary  crops 
the  irrigation  season  seldom  exceeds  four  months  and  in 
many  cases  is  covered  by  two  months. 

208.  Miscellaneous  results. — H.  M.  Wilson,  a  high 
authority  on  irrigation  matters,  presents  the  following  as 
the  duty  of  water  for  1  second-foot  of  water:  In  western 


346  IRRIGATION  PRACTICE 

United  States  it  varies  from  60  to  300  acres;  where  water 
is  most  abundant  it  varies  from  60  to  120  acres;  where 
water  is  less  plentiful  it  varies  from  100  to  150  acres, 
occasionally  rising  to  200  acres;  where  water  is  very  scarce, 
as  in  southern  California,  it  rises  to  300  acres.  There  are 
records  to  show  that  the  duty  of  water  has  reached  even 
1,000  acres  to  the  second-foot  of  water,  but  such  figures 
are  as  yet  exceptional  and  need  not  be  given  serious  con- 
sideration as  part  of  present-day  practical  irrigation 
agriculture. 

Elwood  Mead,  one  of  the  world's  chief  irrigation 
authorities,  declares  that  the  duty  of  water  in  the  United 
States  is  on  the  average  quite  as  high  as  in  the  older 
countries,  but  predicts  that  the  duty  will  be  doubled  as 
more  perfected  methods  of  agriculture  are  adopted. 

F.  H.  Newell,  the  illustrious  director  of  the  Recla- 
mation Service  of  the  United  States,  believes  that  for  good 
farming  an  average  of  12  acre-inches  for  each  acre,  during 
the  irrigation  season,  should  be  enough,  except  for  alfalfa 
and  certain  similar  crops.  This,  for  a  four  month's  irri- 
gation, is  a  duty  of  206  acres.  Newell  further  states  that 
the  duty  of  water  often  reaches  250  to  500  acres  to  the 
second-foot  of  water. 

209.  The  Utah  results. — The  careful  studies  of  the 
Utah  Station  on  the  water  requirements  of  crops  indicate 
that,  when  the  natural  precipitation  is  properly  conserved, 
even  6  acre-inches  an  acre  will  produce  fairly  good  yields 
of  all  the  ordinary  crops.  If  more  water  be  applied  the 
yield  is  smaller  in  proportion.  The  Utah  results  would 
lead  to  the  belief  that  where  the  annual  rainfall  is  from 
12  to  15  inches  a  depth  of  water  from  10  to  20  inches  is 
best  for  ordinary  farm  crops,  and  that  the  best  quantity 
lies  nearer  the  smaller  figure.  A  depth  of  12  inches  prob- 


DUTY  AND  DIVISION  OF  WATER  347 

ably  represents  the  average  requirement  of  ordinary  farm 
crops,  providing  the  water  is  measured  at  the  intake  to  the 
farm.  Should  this  be  increased  to  20  inches  it  would  still 
be  much  less  than  the  quantity  ordinarily  applied.  A 
depth  of  12  acre-inches  equals  a  duty  of  120  acres  per 
second-foot  for  sixty  days,  or  180  acres  for  ninety  days, 
or  240  acres  for  one  hundred  and  twenty  days.  These 
figures  probably  approximate  the  normal  duty  for  western 
America,  under  present  conditions. 

The  new  duty  of  water  must  be  based  upon  all  the 
knowledge  in  the  possession  of  man.  The  water  in  the 
streams  must  be  used  to  cover  the  largest  possible  area 
so  that  more  men  may  be  given  employment  and  more 
families  maintained  upon  the  irrigated  lands. 

THE  MEASUREMENT    OF   WATER 

210.  Need  of  measuring  water. — Farmers  keep  ac- 
counts of  the  area  of  land  under  cultivation,  the  yields  of 
crops  per  acre  and  the  money  received  for  each  bushel  of 
grain  or  ton  of  alfalfa,  but  often  fail  to  keep  track  of  the 
quantity  of  water  used  in  irrigation.  The  whole  discussion 
of  the  preceding  chapters  is,  however,  based  on  the  thesis 
that  irrigation  water  may  be  and  should  be  measured. 
Especially  is  this  necessary  where  water  is  more  valuable 
than  the  land,  and  where  it  is,  therefore,  more  important 
for  the  farmer  to  obtain  a  large  yield  to  the  acre-foot  of 
water  than  to  the  acre  of  land.  Moreover,  if  water,  from 
the  beginning  of  irrigation,  had  been  measured,  less  land 
would  have  become  water-logged  or  subjected  to  the  rise 
of  alkali.  Finally,  there  will  always  be  disputes  about 
water-rights,  and  after  water-rights  are  established  the 
rulings  of  the  courts  must  be  literally  obeyed,  so  that 


348 


IRRIGATION  PRACTICE 


peace  may  prevail  in  irrigation  communities.  What  the 
surveyor  does  in  promoting  peace  as  he  establishes 
boundary  lines  for  fences  between  farms,  the  modern 
irrigation  engineer  does  as  he  determines  the  quantities 
of  water  each  farmer  and  his  neighbor  are  receiving  from 
the  canal  or  river. 

In  the  beginning  of  irrigation  in  this  country,  when 
the  pioneers  were  few  and  had  an  abundance  of  water,  it 
is  evident  that  there  was  not  so  much  need  for  the  meas- 
urement of  water  as  at  the  present  time.  As  more  settlers 


FIG.  95.  A  cable  measuring  station  with  automatic  gauge. 


arrived,  all  the  waters  were  taken  up,  and  there  came  a 
crying  need  for  suitable  devices  for  measuring  and  dividing 
water.  A  perfected  system  of  irrigation  agriculture  cannot 
come  until  measurements  are  made  of  the  flowing  water 
in  the  natural  river  channels,  in  the  main  canals,  in  the 
laterals  and  at  the  headgate  of  each  farm.  In  fact,  the 
measurement  of  water  is  the  great  irrigation  need  of  the 
day,  in  the  face  of  which  all  other  needs  vanish.  All  that 


DUTY  AND  DIVISION  OF  WATER  349. 

has  been  done  in  the  gathering  of  information  concerning 
the  relations  of  soils  and  crops  to  water  is  practically 
useless  unless  the  knowledge  be  applied  under  conditions 
of  carefully  measured  water. 

211.  Who  shall  measure  the  water? — The  company 
controlling  the  irrigation  system  should  conduct  measure- 
ments and  deliver  to  each  farmer  at  his  own  headgate 
and  at  certain  periods  a  definite  number  of  cubic  feet  of 
water.   The  complexity  of  irrigation  agriculture,  however, 
makes  it  evident  that  a  new  kind  of  irrigation  engineer 
must  arrive  who  must  stand  between  the  canal  corpora- 
tion and  the  farmers  drawing  water  from  the  canal.    He 
must  know  enough  engineering  to  measure,  divide  and 
distribute  water  and  to  keep  up  the  system  of  canals  and 
laterals,  and  enough  of  agriculture  to  define  the  quantity 
of  water  for  different  soils  and  crops.    A  big  step  onward 
will  be  taken  when  canal  owners  and  farmers  insist  upon 
such  a  trained  water-master.    However,  hi  this  matter  of 
water-measurement  the  farmer  must  be  independent.   He 
should  understand  the  simple  ways  of  measuring  water 
accurately.    Even  when  the  canal  management  delivers 
definite  quantities  of  water,  it  becomes  the  business  of 
the  farmer  to  distribute  this 'water  correctly  on  the  fields 
of  the  farm,  and  this  can  be  done  only  by  employing  sat- 
isfactory measuring  devices. 

212.  Classes  of  measurement. — Only  under  the  few 
canals  of  moderate  capacity  and  early  water-right,   or 
from  ample  reservoirs,  can  the  farmer  depend  on  receiving 
the  same  quantity  of  water  from  year  to  year.    In  most 
districts  the  total  quantity  of  water  taken  in  by  an  irri- 
gation system  depends  upon  the  quantity  of  water  flowing 
in  the  river  which,  in  turn,  depends  upon  the  varying 
seasons.     Except   for    certain    primary   water-rights,   or 


350 


IRRIGATION  PRACTICE 


small  canals  or  canals  drawn  from  reservoirs,  they  who 
take  water  out  of  a  river  have  right  only  to  a  definite 
proportion  of  the  total  flow.  In  a  dry  as  in  a  wet  year 
this  proportion  remains  the  same.  For  instance,  if  there 


V    %    «•' 

FIG.  96.  Lyman  rectangular  weir. 


are  500  shares  in  such  a  canal  company,  each  share  will 
receive  TO  is  of  the  total  flow  in  the  canal  whether  the 
flow  be  large  or  small. 

There  are,  therefore,  two  classes  of  measuring  devices : 
(1)  Divisors,  for  the  purpose  of  dividing  streams  into 
halves,  quarters  or  other  fractions,  independently  of  the 
volume;  (2)  modules,  for  the  purpose  of  measuring  the 
absolute  volumes  of  water  that  flow  through  canals  or 
ditches.  The  divisors  can  be  made  satisfactorily  only 
after  proper  and  satisfactory  modules  have  been  estab- 
lished. 

A  great  variety  of  water-measuring  devices  exists. 
In  the  beginning  of  modern  irrigation  there  were  no 


DUTY  AND  DIVISION  OF  WATER  351 

special  methods  for  measuring  water.  Ordinary  gates, 
placed  at  the  heads  of  the  laterals,  were  raised  or 
lowered  by  the  water-master  to  send  volumes  of  water, 
equal  to  the  eye,  down  the  laterals  to  farmers  owning 
practically  the  same  water-rights.  Later,  with  the  increas- 
ing value  of  water,  better  measuring  devices  have  been 
adopted. 

The  simplest  devices  for  measuring  the  quantity  of 
water  flowing  in  a  channel  are  those  known  as  weirs  or 
overfalls.  A  board  is  placed  as  a  check  across  the  stream. 
Into  the  board  is  cut  a  notch  through  which  the  water 
flows.  The  weir  method  of  measuring  water  has  been 
investigated  long  and  carefully,  with  the  result  that  in 
some  form  it  may  now  be  used  safely  and  easily  by  the 
farmer.  The  chief  objection  to  the  use  of  weirs  in  irriga- 
tion is  the  tendency  of  the  wen*  to  become  filled  with  silt  if 
the  water  carries  sediment.  When  this  occurs,  the  meas- 
urements are  less  reliable  and  the  weirs  must,  therefore, 
be  cleaned  frequently. 


Three  kinds  of  weirs  are  used  successfully  for  water 
measurement.  First,  the  rectangular  weir,  which  is  best 
known  and  most  certain,  for  it  has  received  most  study 
by  engineers.  It  is  not,  however,  the  simplest,  because 
the  water  flowing  over  the  weir  contracts  at  the  bottom 
and  sides,  and  this  contraction  varies  as  the  depth  of  the 


352  IRRIGATION  PRACTICE 

water  or  the  length  of  the  weir  increases.  The  necessary 
corrections  for  this  variation  complicates  the  use  of  the 
rectangular  weir.  Many  irrigation  engineers,  however, 
well  acquainted  with  irrigation,  insist  that  for  practical 
purposes  no  weir  has  taken  the  place  of  the  rectangular 
weir.  Second,  the  trapezoidal  weir,  which  has  largely 
replaced  the  rectangular  weir  in  irrigation.  The  trape- 
zoidal is  like  the  rectangular  weir,  except  that  the  sides  of 
the  notch  slope  away  slightly,  making  a  trapezoidal, 
instead  of  a  rectangular,  opening  through  which  the  water 
flows.  The  sloping  sides  are  intended  to  correct  auto- 
matically the  loss  of  water  due  to  the  contraction.  Over  a 
trapezoidal  weir  2  feet  long,  all  else  being  equal,  twice  as 
much  water  is  supposed  to  flow  as  over  one  1  foot  long. 
This  is  not  true  of  the  rectangular  weir.  The  first  trape- 
zoidal weir  with  this  purpose  in  view  was  devised  by  the 
Italian  engineer  Cippoletti,  and  the  weir  has  been  named 
the  Cippoletti  weir  by  L.  G.  Carpenter,  of  Colorado, 
who  was  first  to  call  the  attention  of  the  American  public 
to  this  form  of  weir.  In  America,  Canada,  Australia  and 
other  countries  it  is  practically  the  only  weir  used  by  the 
irrigator.  Third,  the  triangular  weir,  the  notch  of  which  is 
in  the  form  of  a  triangle.  Its  chief  advantage  is  that  only 
the  depth  of  water  flowing  over  the  triangle  needs  to  be 
measured.  Very  satisfactory  results  are  obtained  by  the 
use  of  the  triangular  weir,  and  it  is  likely  to  increase  in 
favor.  With  our  present  knowledge,  triangular  weirs 
seem  suitable  chiefly  for  small  streams. 

Recently,  Lyman  has  given  careful  and  exhaustive 
study  to  this  subject,  with  the  result  that  he  has  devised 
methods  whereby  water  may  be  correctly  and  easily 
measured  in  flowing  streams,  without  the  use  of  weirs. 
(Figs.  96,  97.) 


DUTY  AND  DIVISION  OF  WATER  353 

213.  The  Cippoletti  weir. — The  sides  of  the  notch  of 
the  Cippoletti  weir  slope  outward  at  the  rate  of  1  inch 
horizontally,  to  4  niches  vertically.  The  notch  of  the  weir 
is  always  made  with  a  beveled  edge  of  30°  or  more  down 
stream  so  that  the  water  always  flows  over  a  sharp  edge. 
To  maintain  the  sharp  edge,  the  weir  should  be  faced  on 
the  inside,  or  up  stream,  with  iron  strips,  placed  even 
with  the  beveled  edge.  The  distance  from  the  bottom  of  the 
weir  box  to  the  top  of  the 
crest  should  be  at  least 
two  tunes  the  depth  of 
the  water  flowing  over 
the  crest.  The  weir 
should  be  installed  where 
the  approach  of  the  water 
is  straight,  long  and  level. 
As  the  water  passes  over 

the  crest,  it  should  flow  ^  98  appoletti 

very  slowly,  not  more 
than  6  niches  a  second  for  a  weir  6  feet  wide.  The  weir 
must  be  placed  at  right  angles  to  the  stream,  with  the  crest 
absolutely  horizontal.  Provision  should  also  be  made  for 
washing  out  the  accumulating  sediment  by  making  the 
weir  movable,  so  that  it  may  be  raised  from  time  to  time. 
In  many  rivers  or  large  canals  the  weirs  are  movable  and 
are  kept  above  the  stream  except  when  measurements  are 
taken.  Below  the  weir,  where  the  water  falls  over  the 
crest,  there  should  be  sufficient  depth,  so  that  the  water 
below  the  weir  does  not  interfere  with  the  flow  over  the 
crest.  There  should  always  be  a  free  circulation  of  air 
under  the  jet  of  water  falling  over  the  weir.  When  a  weir 
of  known  crest  length  has  once  been  installed,  it  is  neces- 
sary to  determine  only  the  depth  of  water  above  the 
w 


354 


IRRIGATION  PRACTICE 


crest,  some  distance  back  from  the  weir  itself,  where  the 
overfall  has  not  yet  begun  to  curve  the  water  downward. 
Then,  by  the  use  of  tables  (See  Appendix  B),  the  quantity 
of  water  in  cubic  feet  a  second  passing  over  the  weir 


FIG.  99.  Details  of  Cippoletti  weir. 

may  be  determined.  Moreover,  by  use  of  these  tables 
the  size  of  the  weir  necessary  for  a  given  flow  of  water 
may  be  found.  (Figs.  98,  99.) 

However,  even  the  use  of  tables  is  somewhat  unsatis- 
factory and  inconvenient  for  the  farmer  actually  at  work 
in  the  field.  For  that  reason,  plates  have  been  devised, 
that  may  be  screwed  to  the  side  of  the  weir  box,  which 
show  by  inspection  the  number  of  cubic  feet  of  water 
passing  over  the  weir  every  second  of  time.  (See  Fig.  100.) 


DUTY  AND  DIVISION  OF  WATER  355 

Naturally,  a  different  plate  must  be  made  for  each  length 
of  weir.  Once  such  plates  are  installed,  however,  the 
labor  of  reading  weirs  is  reduced  to  a  minimum.  The  whole 
question  of  weir  measurements  is  now  being  critically 
examined  at  the  Colorado  Experiment  Station,  in  cooper- 
ation with  the  United  States  Department  of  Agriculture. 
The  weir  in  some  form  will  undoubtedly  be  the  standard 
measuring  device  of  the  irrigation  world. 

214.  Divisors. — With  the  Cippoletti  weir,  the  division 
of  water  may  be  performed  easily  and  accurately.  Since 
the  slanting  sides  of  the  Cippoletti  weir  allow  for  the 
contraction  of  the  water,  the  quantity  of  water  flowing 
over  any  portion  of  the  crest  is  approximately  equal  to 
that  flowing  over  any  other  similar  portion.  Therefore, 
by  placing  a  partition  below  the  weir  to  divide  the  crest 
into  certain  proportional  parts,  the  stream  itself  is  divided 
into  similar  proportional  parts.  A  beveled  board  or  a 
sharp-edged  partition  of  some  kind  is  placed  at  right  angles 
to  the  crest  and  so  low  as  not  to  interfere  with  the  free 
circulation  of  air  around  the  jet  of  water.  If  the  weir 
crest  is  3  feet  long  and  a  partition  is  placed  1  foot  from 
one  end  of  the  crest,  the  water  is  divided  into  two  parts, 


n°"  ***f"* 

cirrouc-r 


FIG.  100.  Scale  to  be  screwed  on  side  of  Cippoletti  weir.    This  shows  at  a  glance 
the  quantity  of  water  passing  over  the  weir. 


356 


IRRIGATION  PRACTICE 


one  containing  one-third  and  the  other  two-thirds  of  the 
whole  stream.  If  the  partition  is  placed  1J^>  feet  from  the 
end  of  the  crest,  the  flow  is  divided  into  two  equal  streams. 
This  extremely  simple  method  of  dividing  water  seems  to 
give  general  satisfaction.  It  is  frequently  desirable  to 
have  an  adjustable  divisor  to  divide  a 
certain  stream  in  various  ways,  at 
various  times.  Moreover,  two  or  even 
more  partitions  may  be  placed  below 
the  overfall,  to  divide  the  flow  into 
several  streams.  (Fig.  101.) 


FIG.  101.  Divisor  attached  to  Cippoletti  weir. 

Frequently,  it  is  necessary  to  divert  a  constant  quan- 
tity of  water  from  a  large  canal.  For  this  purpose  the 
automatic  weir  suggested  by  Winsor  probably  gives  the 
best  satisfaction.  A  board  with  a  long,  shallow  notch  in 
it  to  act  as  a  spillway  is  placed  lengthwise  in  the  stream 


DUTY  AND  DIVISION  OF  WATER 


357 


FIG.  102.  Turnout  and  measuring  weir. 


near  the  head  of  the  secondary  ditch  to  divert  a  part  of 
the  water  flowing  in  the  main  ditch.  At  the  proper  distance 
down  the  secondary  ditch  an  ordinary  Cippoletti  weir  is 
placed.  The  board  containing  the  spillway  notch  is  raised 
or  lowered  hi  accordance  with  the  quantity  of  water  to  pass 
over  the  weir.  This  device  maintains  the  water  flowing 
over  the  weir  at  practically  the  same  height,  irrespective 
of  the  quantity  of  water 
in  the  main  channel. 
(Figs.  102,  103.) 

THE    DISTRIBUTION 
OF   WATER 


215.  Meaning  of  the 
distribution  of  water. — 
After  the  duty  of  water 
has  been  decided  upon, 
and  the  quantity  of 


FIG.  103.  Device  for  diverting  a  constant 
quantity  of  water. 


358  IRRIGATION  PRACTICE 

water  flowing  into  the  canal  and  its  laterals  has  been 
carefully  measured,  there  yet  remains  the  perplexing  and 
important  problem  of  the  proper  distribution  of  the  canal 
or  reservoir  water  to  the  numerous  farms  of  various  sizes, 
growing  different  crops.  Each  irrigator  must  receive  water 
in  a  quantity  proportional  to  his  interests  in  the  canal,  and 
at  such  a  time  as  will  each  year  insure  him  a  good  crop. 
The  irrigator,  the  owner  of  the  water-right,  knows  only 
one  test  of  the  efficiency  of  the  canal  management — does 
he  have  an  ample  supply  of  water  whenever  needed  by  his 
crops?  The  success  of  an  irrigation  enterprise  depends  on 
the  success  with  which  this  test  is  answered;  that  is,  upon 
the  system  of  distribution  of  water  under  the  canal. 

216.  Methods  of  distribution. — There  are  three  gen- 
eral   methods    of    distributing    irrigation    water    among 
farmers.    First,  a  continuous  flow  of  water  to  the  farm 
during  the  whole  irrigating  season.     Second,   an  inter- 
mittent flow,  which  means  that  the  farmer  gets  a  certain 
flow  of  water  for  a  definite  length  of  time  at  certain  inter- 
vals.   Third,  the  delivery  of  water  to  the  farmer  as  he 
applies  for  it. 

Under  reservoirs,  with  an  ample  supply  of  stored 
water,  any  one  of  these  three  methods  may  be  used. 
Where  canals  are  taken  directly  from  the  rivers  the  first 
two  methods  may  be  used  but  the  third  method  is  prac- 
tically impossible. 

The  method  chosen  for  the  distribution  of  water  may 
affect  greatly  the  duty  of  water  under  the  system,  for  it 
may  determine  the  crops  to  be  grown  and  the  areas  to  be 
devoted  to  each. 

217.  Continuous   flow. — Irrigation   is   not   successful 
unless  the  head  or  volume  of  the  irrigation  stream  is 
sufficiently  large  to  cover  quickly  a  suitable  area  of  land. 


950,000 
900,000 
850,000 
800,000 
750,000 
700,000 
650,000 
600,000 
550,000 
500,000 
450,000 
400,000 
350,000 
300,000 
250,000 
200,000 
150,000 
100,000 
50,000 


ANNUAL  DISCHARGE 
OF  STREAM 
4,202,013. 
ACRE  FEET 


ACRE  FEET 

AVAILABLE  FOR 

IRRIGATION  BY  DIRECT 

DIVERSION 

2,637,094. 

55  PER  CENT  OF 

ANNUAL  FLOW 


ACRE  FEET 

WHICH  MUST 

BE  STORED 

1,564,919. 

45  PERCENT  OF 

ANNUAL  FLOW 


FIG.  104.  The  need  of  storing  water  in  reservoirs.    (Yakima  River.) 

(359) 


360  IRRIGATION  PRACTICE 

If  the  volume  is  very  small,  too  large  a  proportion  of  the 
water  is  lost  by  evaporation  during  the  long  time  required 
to  cover  the  land  with  water.  The  method  of  continuous 
flow,  which  means  that  a  stream  of  the  same  volume 
enters  the  farm  from  the  beginning  to  the  end  of  the  irri- 
gation season  is  successful  only  if  the  stream  has  a  suffi- 
cient head,  say  from  1  to  2  second-feet.  If  smaller  than 
this  the  method  of  continuous  flow  is  not  usually  satis- 
factory. A  large  farm  of  from  100  to  300  acres  may 
utilize  so  large  a  continuous  stream.  On  small  farms  with 
small  water  supplies,  the  method  of  continuous  flow  is 
utterly  unsatisfactory.  A  chief  objection,  even  on  large 
farms,  to  the  method  of  continuous  flow,  is  that,  under  it, 
irrigation  must  always  be  going  on.  The  method  of  con- 
tinuous flow  is  of  real  value  only  when  the  farm  is  a  mini- 
ature complete  irrigation  system,  representing  the  diver- 
sity of  crops  and  conditions  under  the  whole  canal  system; 
for  only  when  this  condition  exists  can  the  water  be  used 
to  advantage  from  the  beginning  to  the  end  of  the  season. 
There  is  always  more  land  than  water  in  the  irrigated 
sections.  A  man  having  a  continuous  stream  of  water 
throughout  the  season  would  probably  plant  one-half  of 
his  farm  to  grainsN  and  other  early-maturing  crops,  and  the 
other  half  to  potatoes,  beets  or  other  late-maturing  crops. 
In  the  early  season  the  water  would  be  used  chiefly  on  the 
early  crops;  in  the  later  season  on  the  later  crops.  By  such 
methods,  the  continuous  flow  may  be  made  to  cover  larger 
areas  than  can  the  intermittent  method.  In  practice,  the 
distribution  of  water  by  continuous  flow  is  carried  on  as 
follows:  Ten  second-feet  are  carried  by  a  canal  for  the 
use  of  1,500  acres  divided  into  several  farms.  Laterals 
are  made  to  each  farm,  in  which  is  carried  the  proper  pro- 
portion of  water  for  that  farm.  Thus,  a  farm  of  150  acres, 


DUTY  AND  DIVISION  OF  WATER  361 

one-tenth  of  the  total  area,  would  receive  a  continuous 
flow  throughout  the  season  of  one-tenth  of  the  total  flow, 
or  1  second-foot.  A  farm  of  50  acres,  under  this  system, 
would  receive  a  continuous  flow  of  one-third  of  a  second- 
foot.  The  system  is  exceedingly  simple  after  the  laterals 
and  dividing  contrivances  have  once  been  established. 
The  burden  of  the  method  falls  upon  the  farmer  who  must 
use  the  water  every  day  and  night  throughout  the  season. 

218.  Continuous  rotation. — The  method  of  distributing 
water  by  rotation  is  by  far  the  most  satisfactory.  In 
America,  it  was  introduced  by  the  irrigation  pioneers, 
and  since  that  time  has  been  tried  out  thoroughly  hi  every 
section  of  the  country.  It  is  the  standard  method  of 
water  distribution  in  Asia,  Africa,  Europe  and  Australia. 
Every  great  irrigation  enterprise  has  either  adopted  the 
method  of  rotation  or  is  planning  to  adopt  it. 

By  the  method  of  continuous  rotation  the  farmer 
receives  a  stream  carrying  a  rather  large  head  or  volume 
of  water  for  a  certain  definite  number  of  hours,  after 
which  no  water  is  at  his  disposal  until  his  turn  comes 
again,  when  a  similar  stream  is  received  for  the  same 
length  of  time.  The  relatively  large  streams  of  water 
thus  supplied  give  the  small  farmers  the  advantage  of 
the  larger  farmers,  of  applying  the  water  to  the  land  hi 
the  shortest  possible  time.  Moreover,  the  farmer  is  re- 
lieved of  the  strain  of  constant  irrigation.  During  the 
time  that  the  stream  is  at  the  farmer's  disposal,  he  can 
give  himself  wholly  to  the  work  of  irrigation;  when  that 
work  is  done,  he  may  turn  to  some  other  farm  operation. 
Experience  has  shown  this  to  be  most  satisfactory  to  the 
farmer. 

This  method  tends  to  eliminate  the  waste  of  water. 
Under  the  method  of  continubus  flow,  the  steady  care  of 


362  IRRIGATION  PRACTICE 

the  water  becomes  so  burdensome  that  much  of  the  water 
is  often  allowed  to  go  to  waste.  The  method  of  rotation, 
on  the  other  hand,  develops  a  spirit  of  using  water  care- 
fully, since  the  time  during  which  it  is  available  for  the 
farmer  is  relatively  short  and  the  work  must  be  done  at 
that  time  or  not  at  all  until  the  next  turn.  The  farmer 
under  the  rotation  method  receives  the  water  schedule 
early  in  the  spring,  and  knows  in  advance  the  dates  on 
which  he  will  receive  water.  He  may  then  plan  much  of 
his  work  for  summer,  and  because  of  this  system  can 
make  his  days  more  pleasant  and  profitable.  Perhaps  the 
greatest  argument  for  the  method  of  rotation  is  that 
it  gives  the  small  farmer  an  equal  chance  with  the  large 
farmer.  Under  the  method  of  continuous  flow  the  farmer 
owning  10  acres  would  be  obliged  to  spend  as  much,  or 
possibly  more,  time  in  irrigation  as  would  the  man  who 
owned  100  or  more  acres.  Under  the  method  of  continuous 
rotation,  the  small  farmer  works  as  hard  as  the  large 
farmer,  during  a  time  in  proportion  to  the  acreage  that 
he  possesses. 

The  application  of  the  method  of  rotation  is  simple  and 
varies  only  slightly  under  varying  conditions.  In  the 
main  canal,  particularly  if  it  is  taken  directly  from  the 
river,  water  flows  continuously;  and  the  chief  laterals 
likewise  carry  continuous  flows  of  water.  The  laterals  are 
divided  and  sub-divided  into  smaller  streams,  until  the 
quantity  of  water  flowing  continuously  in  each  meets 
the  requirements  of  the  area  of  land  under  the  stream,  in 
accordance  with  the  duty  of  water  prevailing  under  the 
system.  Let  it  be  assumed  that  the  duty  of  water  under  a 
canal  system  is  100  acres  to  the  second-foot,  during  the 
irrigation  season,  and  that  at  each  application  a  depth  of 
water  not  more  than  4  inches  should  be  applied.  A  certain 


DUTY  AND   DIVISION  OF   WATER  363 

lateral  under  this  system  carries  2  second-feet  of  water 
continuously,  and  is,  therefore,  to  be  reserved  for  200 
acres.  This  means  that  the  whole  200  acres  could  be 
covered  by  this  stream,  to  a  depth  of  4  inches,  every  six- 
teen and  two-thirds  days.  In  other  words,  each  farm 
under  this  lateral  would  receive  its  allotment  of  water 
every  sixteen  and  two-third  days.  If  the  200  acres  under 
this  lateral  consist  of  six  farms  of  5,  10,  20,  25,  40  and 
100  acres  respectively,  it  may  easily  be  calculated  that 
they  would  receive  water  every  sixteen  and  two-third 
days  as  follows: 

Length  of  irrigation  period  (every  16% 
Area  of  farm  days,  or  400  hours) 

5  acres  10  hours 

10  20 

20  40 

25  50 

40  80 

100  200 

200     "  400     " 

If  the  stream  were  larger,  the  time  for  each  farm  would 
be  correspondingly  decreased.  Such  a  system  may  be 
followed  easily  by  the  water-master  and  is  readily  under- 
stood by  the  farmer. 

Another  application  of  the  rotation  method  is  to  fill 
the  mam  laterals  in  rotation.  One  or  a  few  laterals  are 
given  all  the  water  of  the  canal  for  a  certain  number  of 
days;  then  another  set  of  laterals,  and  so  on,  until  the 
rotation  has  been  accomplished.  This  system  is  not  so 
satisfactory  to  the  farmer  as  the  preceding  one,  because 
a  whole  district  is  for  a  time  without  water,  when  the 
neighboring  district  has  an  abundance.  Under  the  first 
system  all  districts  under  the  canal  are  at  all  times  doing 
some  irrigating,  and  the  presence  of  the  water  gives  the 
farmer  a  sense  of  security. 


364  IRRIGATION  PRACTICE 

Still  another  application  of  the  method  of  rotation  is 
found  where  city  lots  are  watered  for  the  purpose  of  main- 
taining home  gardens,  which  usually,  because  of  less  care- 
ful cultivation,  require  water  very  frequently.  Under  this 
method  the  flow  of  water  is  divided  into  many  small 
streams  that  make  it  possible  to  irrigate  every  week  or 
every  two  weeks. 

Each  farmer,  under  the  rotation  method  of  distribution, 
is  notified  at  the  beginning  of  the  irrigation  season  of  the 
size  of  the  stream  allotted,  and  the  time  and  frequency 
of  its  use.  The  farmer  is  sometimes  permitted  to  turn  the 
water  into  his  own  ditch  at  the  hour  assigned,  but  the 
better  plan  is  to  allow  a  regularly  employed  water- 
master  or  ditch-tender  to  open  or  close  all  gates  and  to 
divert  water  to  or  from  farms.  The  farmers  under  a 
lateral  frequently  organize,  and  as  a  company  manage 
the  water  from  the  lateral,  exactly  as  the  laterals  are 
managed  by  the  canal  company.  When  this  is  done,  the 
responsibility  for  the  ultimate  distribution  of  the  water 
rests  upon  the  group  of  farmers  living  under  the  lateral. 
Such  lateral  organizations  are  proving  very  satisfactory, 
and  it  may  be  that  they  will  increase  until  the  canal 
managements  will  need  to  exercise  no  further  jurisdiction 
over  the  distribution  of  water  after  it  has  once  been 
turned  into  the  laterals.  Such  a  lateral  organization 
determines  for  itself  the  method  of  water  distribution  to 
be  used. 

219.  Distribution  on  application. — This  method  means 
that  water  flows  to  a  farm  only  at  the  request  of  the 
farmer.  The  method  is  practicable  only  under  reservoirs, 
or  canals  that  are  always  filled  with  water.  Under  reser- 
voirs the  farmer  may  be  said  to  own  a  definite  quantity 
of  stored  water  upon  which  he  may  draw  as  he  chooses, 


DUTY  AND  DIVISION  OF  WATER  365 

just  as  he  does  with  his  money  in  the  bank.  The  chief 
objection  to  this  method  of  distribution  is  that  if  many 
farmers  should  call  for  water  at  the  same  time,  more 
water  might  be  demanded  than  the  canals  could  carry. 
When  this  method  is  used  under  ordinary  diversion  canals, 
it  is  generally  for  the  purpose  of  compelling  the  most 
economical  use  of  water.  The  tendency  of  the  irrigator  to 
use  too  much  water  is  increased  whenever  a  continuous 
flow  of  water  is  supplied,  or  under  methods  of  rotation, 
when  water  is  given  for  longer  periods  than  is  actually 
needed.  If  the  irrigator  feels  that  he  has  a  limited  quantity 
of  water  in  the  system,  on  which  he  may  draw  at  will,  he 
is  more  likely  to  practice  greater  irrigation  economy,  and 
the  surplus  water  may  then  be  applied  beneficially  else- 
where. The  method  of  distributing  water  on  the  appli- 
cation of  the  farmer  is  an  ideal  system,  but  of  extremely 
limited  application.  Even  under  reservoir  conditions  it 
will  probably  be  found  that  the  rotation  method  will  in 
the  end  give  the  greatest  satisfaction. 

220.  Organization  for  distribution. — The  proper  dis- 
tribution of  water  from  great  canals  can  be  accomplished 
only  by  an  organization  for  the  purpose.  In  the  early 
irrigation  days,  when  water  was  relatively  plentiful  and 
the  population  small,  little  attention  was  given  to  super- 
vision. Each  man  drew  what  he  needed  from  the  coopera- 
tive canal.  The  increasing  value  of  water  has  made  the 
the  proper  distribution  of  water  more  and  more  important. 
Large  canals  that  serve  3,000  to  20,000  acres,  especially, 
are  justified  in  exercising  very  careful  supervision  of  the 
distribution  of  the  water.  It  should  be  insisted  upon  by 
those  who  have  the  best  interests  of  the  system  at  heart. 
Experience  points  to  the  conclusion  that  the  success  of 
an  irrigation  system  is  in  direct  proportion  to  the  super- 


366  IRRIGATION  PRACTICE 

vision  given  to  the  distribution  of  the  water  and  to  the 
maintenance  of  the  system. 

Some  sort  of  supervision  exists  under  practically  all 
canals,  but  it  is  exceedingly  varied.  Under  the  Davis  and 
Weber  Counties  Canal  in  Utah,  serving  12,000  acres,  divided 
among  520  farmers,  four  men  only  are  employed  to  dis- 
tribute the  water  equitably.  Under  the  Farmers'  Canal 
in  Montana,  serving  15,000  acres,  owned  by  sixty  farmers, 
two  men  on  part  time  supervise  the  distribution  of  the 
water.  On  the  other  hand,  the  Gage  Canal  in  California, 
serving  only  9,000  acres,  finds  it  profitable  to  maintain  a 
chief  engineer  and  six  other  men  for  the  proper  distribution 
of  the  water  flowing  through  the  canal  and  for  the  main- 
tenance of  the  system  itself.  The  same  force  of  men  can 
usually  supervise  the  distribution  of  the  water  during  the 
irrigation  season  and  maintain  the  system  itself. 

The  head  of  the  organization  for  water  distribution 
and  canal  maintenance,  called,  possibly,  the  manager  or 
superintendent,  should  be  an  irrigation  engineer.  He 
should  be,  however,  an  engineer  of  a  new  type — one  who 
understands  enough  of  engineering  to  maintain  in  a  high 
state  of  excellence  the  dams,  canals,  laterals  and  gates  of 
the  irrigation  system,  and  who  understands  enough  of 
modern  irrigation  agriculture  to  direct  the  use  of  the 
water  for  the  production  of  crops  under  the  canal  system. 
To  such  a  man  belongs  justly  the  title  of  irrigation  engi- 
neer. If  one  canal  company  does  not  feel  itself  wealthy 
enough  to  maintain  such  a  trained  superintendent,  it  is 
often  possible  for  adjoining  canal  systems  to  employ  the 
same  superintendent  who  can  be  assisted  by  water-mas- 
ters from  the  respective  systems.  Much  money  could  be 
saved  in  legal  and  engineering  services  if  such  permanent 
expert  help  were  employed. 


DUTY  AND  DIVISION  OF  WATER  367 

This  chief  worker  should  be  assisted  by  water-masters 
to  whom  various  duties  could  be  assigned.  Some,  taking 
the  place  of  the  old  ditch-rider,  should  supervise  the 
admission  of  the  right  quantity  of  water  from  the  main 
canal  into  each  lateral;  others  could  well  be  used  to 
supervise  the  up-keep  of  the  main  canal  and  its  laterals. 
Ditch-tenders,  as  assistants  to  the  water-masters,  should 
be  employed,  if  necessary,  to  supervise  the  farmers'  ditches 
drawing  water  from  the  laterals.  The  water-masters  and 
the  ditch-tenders  should  be  somewhat  trained  for  their 
work.  Especially  should  they  understand  water  units, 
the  relation  between  soils,  crops  and  water,  and  the 
common  methods  of  measuring  and  dividing  water. 
Moreover,  they  should  be  experienced  in  the  practice  of 
irrigation  so  that  the  farmers7  side  may  be  understood 
by  them. 

Where  the  farmers  under  a  lateral  have  formed  a  lateral 
organization  they  could  well  employ  their  own  water- 
master,  who,  like  the  company  water-masters,  should  be 
trained  for  the  work.  The  day  of  the  untrained  man  for 
water-distribution  has  passed.  The  superintendent,  water- 
masters  and  ditch-tenders,  must  know  their  work,  and 
must  especially  be  familiar  with  the  use  of  water  in  irri- 
gation. Then  will  the  work  be  done  well. 

The  cost  of  such  supervision  of  the  distribution  of 
water  and  of  the  maintenance  of  the  system,  including 
the  keeping  of  records,  is  not  great.  According  to  Adams, 
for  thirteen  of  the  best-known  canals  in  western  America, 
it  varies  from  9  cents  to  $1.30  an  acre,  with  an  average 
of  41  ^2  cents  an  acre,  a  year.  This  is  not  at  all  prohibitive 
if  one  considers  that  by  the  unwise  or  dishonest  distribution 
of  water  crop  failures  or  crop  diminutions  may  easily 
occur. 


368  IRRIGATION  PRACTICE 

221.  Regulations  and  records. — Irrigation  under  the 
best  conditions  is  complex.  If  the  best  results  are  to  be 
obtained  from  an  irrigation  system,  careful  regulations 
must  be  established  and  published,  and  careful  records 
must  be  kept.  It  is  a  common  fault  that  the  farmers  are 
not  kept  in  full  touch  with  the  plans  under  which  the 
system  is  operated,  including  the  duty,  measurement 
and  distribution  of  water.  Full  information  concerning 
the  rules  of  the  system,  including  its  relation  to  the 
farmer,  should  be  printed  and  distributed  to  every  farmer 
under  the  system.  The  greater  the  publicity  given  the 
operations  of  the  canal  management,  whether  consisting 
of  farmers  or  capitalists,  the  less  friction  will  accompany 
the  work. 

The  records  of  the  system  should  be  as  orderly  as  those 
of  the  best  commercial  establishments.  Water  has  a  de- 
finite cash  value;  and  it  should  be  traced  as  carefully  as 
is  any  other  valuable  commodity.  At  regular  intervals 
the  flow  of  water  into  the  main  canal  and  into  each  of  the 
laterals,  and  as  far  as  possible  on  to  the  farms,  should  be 
carefully  measured.  Excellent  type  records  may  be  found 
in  Bulletin  No.  229  of  the  Office  of  Experiment  Stations, 
United  States  Department  of  Agriculture,  entitled 
"Delivery  of  Water  to  Irrigators,"  by  Frank  Adams.  The 
superintendent,  water-masters  and  ditch-tenders  should  all 
be  taught  to  make  such  records,  and  should  be  charged 
with  the  duty  of  making  such  permanent  records.  In 
avoiding  the  characteristic  irrigation  disputes,  such 
records  would  be  of  inestimable  value.  The  keeping  of 
accurate  records  by  irrigation  systems  would  also  help 
greatly  to  increase  the  duty  of  water.  Both  crop  and 
water  records  should  be  kept.  The  want  of  record-keeping 
is  largely  responsible  for  our  faulty  irrigation  methods. 


DUTY  AND  DIVISION  OF  WATER  369 

REFERENCES 

ADAMS;  FRANK.  Delivery  of  Water  to  Irrigators.  United  States 
Department  of  Agriculture,  Office  of  Experiment  Stations, 
Bulletin  No.  229  (1910). 

BARK,  DON  H.  Duty  of  Water  Investigations.  Ninth  Biennial 
Report  of  the  State  Engineer  of  Idaho,  1911-12. 

BUCKLEY,  ROBERT  BURTON.  Facts,  Figures  and  Formulae  for  Irri- 
gation Engineers  (1908). 

BUCKLEY,  ROBERT  BURTON.  The  Irrigation  Works  of  India.  Second 
edition  (1905). 

CARPENTER,  L.  G.  On  the  Measurement  and  Division  of  Water. 
Fourth  edition.  Colorado  Experiment  Station,  Bulletin  No. 
150  (1910). 

CONE,  V.  M.  Hydraulic  Laboratory  for  Irrigation  Investigations. 
Fort  Collins,  Colorado.  Engineering  News,  Vol.  LXX,  No.  10, 
p.  662  (1913). 

CONE,  V.  M.,  TRIMBLE,  R.  E.,  and  JONES,  P.  S.  Frictional  Resist- 
ance in  Artificial  Waterways.  Colorado  Experiment  Station, 
Bulletin  No.  194  (1914). 

FLYNN,  P.  J.   Irrigation  Canals,  etc.  (1892). 

HORTON,  ROBERT  E.  Weir  Experiments,  Coefficients  and  Formulae. 
United  States  Geological  Survey,  Water  Supply  Papers,  No. 
200  (1907). 

LYMAN,  RICHARD  R.  Why  Irrigation  Water  Should  be  Measured. 
Bulletin  International  Irrigation  Congress,  Vol.  I,  p.  63  (1912). 

LYMAN,  RICHARD  R.  Measurement  of  Flowing  Streams.  Utah 
Engineering  Experiment  Station,  University  of  Utah,  Bulletin 
No.  5  (1912). 

LYMAN,  RICHARD  R.  Measurement  of  the  Flow  of  Streams.  Proceed- 
ings of  American  Society  of  Civil  Engineers,  Vol.  XXXIX,  p. 
1913  (1913). 

MEAD,  ELWOOD.  Irrigation  in  northern  Italy.  United  States 
Department  of  Agriculture,  Office  of  Experiment  Stations, 
Bulletins  Nos.  144  (1904)  and  190  (1907). 

MEAD,  ELWOOD.  Irrigation  Institutions.  The  Macmillan  Company 
(1903). 

NEWELL,  F.  H.   Irrigation.   Crowell  &  Co.  (1906). 
X 


370  IRRIGATION  PRACTICE 

TANNATT,  E.  TAPPAN,  and  KNEALE,  R.  D.  Measurement  of  Water. 
Montana  Experiment  Station,  Bulletin  No.  72  (1908). 

TEELE,  R.  P.  Review  of  Ten  Years  of  Irrigation  Investigations. 
United  States  Department  of  Agriculture,  Office  of  Experiment 
Stations,  Annual  Report  (1908). 

TEELE,  R.  P.  The  State  Engineer  and  His  Relation  to  Irrigation. 
United  States  Department  of  Agriculture,  Office  of  Experi- 
ment Stations,  Bulletin  No.  168  (1906). 

UNITED  STATES  RECLAMATION  SERVICE.  Operation  and  Mainte- 
nance Use-Book  (1913). 

WIDTSOE,  J.  A.,  and  MERRILL,  L.  A.  The  Yields  of  Crops  with 
Various  Quantities  of  Irrigation  Water.  Utah  Experiment 
Station,  Bulletin  No.  117  (1912). 

WILLCOX,  WILLIAM.  The  Nile  Reservoir  Dam  at  Assuan  (1903). 

WILLCOX,  WILLIAM.   The  Nile  in  1904.    1904  (E.  &  F.  N.  Spon.) 

WILSON,  HERBERT  M.  Irrigation  in  India.  United  States  Geologi- 
cal Survey,  Water  Supply  and  Irrigation  Papers,  No.  87  (1903). 

WILSON,  HERBERT  M.  Manual  of  Irrigation  Engineering.  Third 
edition  (1899).  Wiley  &  Sons. 

WINSOR,  L.  M.  Measurement  and  Distribution  of  Water.  Utah 
Experiment  Station,  Circular  No.  6  (1912). 


CHAPTER  XVIII 
OVER-IRRIGATION  AND  ALKALI 

OVEK-IRRIGATION  and  alkali  are  the  two  chief  evils 
that  endanger  irrigation  as  a  permanent  system  of  agri- 
culture. These  result  from  the  unwise  use  of  water  and 
from  peculiar  soil  conditions  that  may  be  aggravated  by 
excessive  irrigation. 

222.  Seepage  from  reservoirs  and  canals. — Soil  is  a 
porous  mass.  Water  added  to  the  soil  forms  a  film  around 
the  soil  particles  which  thickens  as  more  water  is  added, 
until  the  film  becomes  so  thick  that  the  liquid  water 
slides  through  the  capillary  spaces  to  the  greater  depths 
of  the  soil.  When  the  annual  rainfall  is  from  20  to  30 
inches,  approximately  one-half  of  it  seeps  through  the 
soil  beyond  the  reach  of  plants.  Under  a  high  rainfall 
more  is  lost.  This  seepage  continues  until  the  water 
reaches  an  impervious  layer  of  rock,  clay  or  other  sub- 
stance, where  a  permanent  water  table  is  formed;  and  the 
more  water  is  added  from  above,  the  thicker  becomes  the 
water  table.  It  does  not  necessarily  stand  still,  but  usually 
flows  gradually  hi  some  direction  depending  upon  the 
inclination  of  the  impervious  bottom.  According  to  the 
most  recent  estimates  there  is  such  a  layer  of  water  100 
feet  thick,  on  the  average,  under  the  whole  surface  of  the 
earth. 

Much  of  this  subterranean  water  is  derived  from  the 
rainfall  directly;  much  water  seeps  also  from  the  river 
beds,  which  are  covered  with  water  practically  the  whole 

(371) 


372  IRRIGATION  PRACTICE 

year.  There  is  always  a  possibility,  also,  of  seepage  from 
reservoirs  for  the  storage  of  water.  If  the  reservoirs  are 
well  silted  large  losses  will  not  occur.  A  reservoir  from 
which  a  depth  of  water  of  not  more  than  2  feet  is  lost 
annually  is  said  to  be  practically  impervious.  The  smaller 
the  reservoir,  the  better  silted  it  is,  and,  therefore,  the 
smaller  the  loss  of  water  from  it.  From  canals,  also,  there 
are  large  losses  of  water  by  seepage.  For  instance,  the 
United  States  Irrigation  Investigations  have  found  that, 
as  an  average  for  all  canals  investigated,  the  loss  by  seepage 
was  5.77  per  cent  of  the  total  water  carried,  for  every 
mile  of  canal.  The  aggregate  loss  of  water  by  seepage 
from  canals  must,  therefore,  be  tremendous.  Individual 
canals  differ,  however,  greatly  in  this  respect.  In  the 
government  investigations,  the  losses  from  canals  varied 
from  none  to  60  per  cent  of  the  total  quantity  of  water 
carried,  for  each  mile  of  canal.  If  a  canal  passes  over  a 
rocky  ledge,  much  water  may  be  lost  through  cracks  and 
crevices.  Canals  passing  over  gravelly  soils  lose  most;  over 
sandy  soils,  nearly  as  much,  and  over  heavy  clay  soils, 
least  water.  New  canals  always  lose  more  water  by 
seepage  than  do  old  ones,  because  silting  and  settling 
has  not  been  fully  established.  Small  canals  lose  propor- 
tionately more  than  large  ones,  and  canals  not  used  in  the 
winter  lose  less  than  those  filled  with  water  throughout 
the  year,  although  at  the  time  of  opening  the  canals  in 
the  spring,  before  silting  has  gone  on,  the  loss  is  greater. 
On  the  average,  30  per  cent  of  the  water  taken  in  at  the 
head-gates  of  irrigation  canals  is  lost  by  seepage  from 
the  canals  themselves.  In  comparison  with  this  great  loss 
all  other  losses  are  small.  The  loss  of  water  by  evaporation, 
for  instance,  is  ordinarily  less  than  15  per  cent  of  the  loss 
due  to  seepage.  Carpenter  concluded  that  the  water  lost 


OVER-IRRIGATION  AND  ALKALI  373 

from  canals  in  one  day  is  sometimes  equivalent  to  a  depth 
of  20  feet  and  is  seldom  less  than  3  inches  over  the  whole 
canal  surface. 

The  laterals  of  canals  are  subject  to  similar  losses. 
Every  irrigation  farmer  knows  that  though  the  flow  into 
the  lateral  at  the  head-gate  may  be  ample,  frequently  not 
enough  water  reaches  the  farm.  Practically,  another 
third  of  the  water  taken  in  at  the  head-gate  is  gone 
before  it  reaches  the  farmer. 

223.  Loss  from  excessive  irrigation. — Water  is  lost 
by  seepage  on  the  farm  itself,  for  the  common  practice  is 
to  irrigate  land  too  heavily.  When  more  than  5  inches  of 
water  are  added  to  the  soil  in  any  one  irrigation,  there  is 
usually  a  loss  by  seepage;  yet,  on  a  great  many  farms, 
twice  that  much  water  is  applied  at  one  irrigation,  pro- 
viding it  is  available  and  the  soil  can  be  made  to  absorb 
it.  Evil  follows  such  excessive  irrigations,  especially  if 
they  succeed  each  other  at  short  intervals.  Farmers  who 
misunderstand  the  use  of  water  usually  apply  as  much  as 
possible,  as  frequently  as  possible,  and  urge  upon  the  canal 
managers  the  necessity  of  having  free  access  to  water. 
An  irrigation  applied  to  the  soil  before  the  plant  roots 
have  had  time  to  remove  the  water  added  in  the  previous 
irrigation  retards  the  growth  of  the  crop,  and  soaks  down 
the  soil  to  increase  the  standing  water  table.  The  loss  of 
water  due  to  excessive  use  of  the  water  on  the  farm  is 
often  very  large.  It  may  safely  be  estimated  that  one- 
half  of  the  water  taken  in  at  the  head-gate  of  the  canal 
is  lost  by  percolation  from  canals,  ditches  and  excessive 
irrigation.  This  is  an  awful  waste  when  the  great  cost  of 
irrigation  structures  and  the  vast  areas  of  arid  land  are 
considered.  The  old  idea  that  irrigation  should  take  the 
place  of  tillage  must  be  fought  vigorously. 


374 


IRRIGATION  PRACTICE 


224.  Ground  water. — The  seepage  losses  from  reser- 
voirs, canals,  laterals  and  farms  increase  the  depth  of  the 
ground  water.  Consequently,  in  irrigated  sections,  where 
such  losses  go  on  uninterruptedly,  water  rises  slowly  but 
steadily  until  wells  that  were  dug  50  to  100  feet  deep  to 
reach  water,  now  have  the  water  table  within  3  to  10  feet 
from  the  surface.  This  great  layer  of  ground  water  flows 
along  the  impervious  layer  upon  which  it  rests,  usually 


fion  or  we.//s  a/on g  rru/f  A 


FIG.  105.  Rise  of  ground  water  from  irrigation. 

slowly,  but  sometimes  rapidly.  Carpenter  found  in  one 
place  that  the  underground  movement  of  water  reached 
a  rate  of  1  mile  an  hour.  According  to  the  underground 
structure  of  clay  deposits,  hardpan  or  bedrock,  this  water 
comes  out  somewhere,  usually  in  the  lower-lying  lands,  to 
form  springs,  bogs  and  water-logged  lands.  The  first 
irrigation  settlements  were  often  made  on  the  lower  lands, 
where  the  natural  seepage  made  green  spots  of  grass  or 
clumps  of  trees,  that  looked  inviting  to  the  pioneers.  As 
the  higher-lying  irrigation  canals  were  taken  out,  the 
seepage  from  them  soon  converted  these  green  spots, 


OVER-IRRIGATION  AND  ALKALI  375 

the  natural  drainage  outlets  of  the  district,  into  water- 
logged lands  which  had  to  be  abandoned.  In  that  way  the 
danger  of  seepage  has  from  the  beginning  been  called  to 
the  attention  of  the  irrigation  communities. 

True,  the  water  that  seeps  from  the  canals  and  the 
farms  is  not  wholly  lost.  Some  finds  its  way  into  the 
lower  canals  or  rivers  and  is  used  elsewhere.  The  "lost 
rivers"  of  the  West  are  examples  of  this  condition.  The 
Sevier  River  of  Utah  flows  full  near  its  head,  and  gradually 
disappears  until  it  is  nearly  dry;  but,  lower  down,  the 
water  reappears  and  the  river  flows  full  again.  Where  the 
underflow  can  be  caught,  canals  have  been  built  for  the 
purpose.  Moreover,  the  underground  waters  of  the 
country,  especially  in  the  arid  West,  will  be  used  more 
and  more  as  irrigation  by  pumping  becomes  better  under- 
stood. Under  the  best  of  conditions,  however,  much  of 
the  water  that  disappears  by  seepage  is  permanently 
lost.  Seepage  must  be  reduced  to  the  minimum. 

225.  Comparison  with  humid  areas. — The  danger  from 
unnecessary  seepage,  due  to  excessive  irrigation  and  canal 
losses,  is  certainly  great;  but,  the  area  of  resulting  water- 
logged lands  is  not  nearly  so  great  in  proportion  to  the 
land  surface  as  are  the  water-logged  lands  of  humid  re- 
gions. According  to  the  last  government  census,  the 
swamp  and  marsh  lands  east  of  the  Rocky  Mountains, 
subject  to  reclamation,  cover  an  area  of  77,000,000  acres — 
nearly  equal  to  the  combined  area  of  Illinois,  Indiana  and 
Ohio.  This  area  of  swamp  and  marsh  land  varies  roughly 
with  the  rainfall,  which  is  another  proof  of  the  doctrine 
that  such  lands  are  determined  by  the  quantity  of  water 
brought  upon  the  soil  surface.  The  water-logged  lands  of 
the  irrigated  regions  form  a  very  small  fraction  of  the 
cultivable  land,  and  it  lies  within  the  power  of  the  irri- 


376 


IRRIGATION  PRACTICE 


gator  to  reduce  this  area  by  wiser  methods  of  conducting 
and  using  water. 

226.  Lined  ditches — a  remedy. — The  chief  danger  of 
seepage  will  remain  with  the  canals  and  laterals,  for  it  is 


FIG.  106.  Chain  puddler.    Used  in  making  canals  watertight. 

relatively  easy  to  control  the  quantity  of  water  used  on 
the  land.  The  first  obvious  remedy  against  seepage  is, 
therefore,  to  make  the  ditches  more  impervious.  A  canal 
carrying  clear  water  will  not  of  itself  become  impervious, 
but  a  canal  carrying  muddy  water  will  receive  the  settlings, 
often  to  such  a  degree  as  to  reduce  or  even  to  stop  the 
seepage.  Moreover,  the  leaks  due  to  layers  of  gravel,  sand 
or  open  rock,  over  which  canals  pass,  should  be  stopped 
by  the  application  of  clay  or  some  other  impervious 
material.  Very  often,  it  is  advisable  to  line  the  whole 
canal  with  impervious  materials  or  to  build  flumes  or 
pipes  to  take  the  place  of  the  canal.  The  first  expense 
seems  large,  but  the  annual  saving  of  water  and  the 


OV RE-IRRIGATION  AND  ALKALI 


377 


reduction  of  the  area  of  lower  water-logged  lands  justify 
the  expenditure.  The  many  materials  used  for  this  pur- 
pose are  discussed  in  special  books  on  the  subject. 

The  oldest  method  of  lining  ditches  is  by  masonry,  the 
first  cost  of  which  is  not,  by  any  means,  the  most  expensive, 
but  requires  relatively  skilled  labor,  and  later  considerable 
upkeep.  Cement  concrete,  though  it  is  most  expensive,  is 
becoming  the  favorite  material  for  lining  ditches,  for  under 
good  supervision,  it  can  be  installed  rapidly  and  with 
ordinarily  available  labor.  The  great  objection  to  cement 
concrete  linings  is  that  in  cold  districts  it  is  likely  to  break 
unless  carefully  covered  with  earth  or  sand.  Meanwhile 
large,  cement-lined  canals,  even  in  districts  of  very  cold 
winters,  are  giving  excellent  satisfaction. 

Crude  mineral  oil  is  also  a  favorite  material  for  lining 
irrigation  ditches.  It  is  heated  and  while  still  hot  is  sprink- 
led with  an  ordinary  road  sprinkler  over  the  bottom  and 
sides  of  the  canal.  It  is  then  harrowed  in,  usually  with  a 
chain  puddler.  This  treatment  reduces,  largely,  the 
seepage.  The  older  method  of  puddling  thoroughly  the 
bottom  and  sides  of  the  canal  with  clay  is  often  the 


FIG.  107.  Modified  chain  puddler. 


378  IRRIGATION  PRACTICE 

cheapest  and  most  satisfactory  where  the  materials  are 
near  at  hand,  but  the  effects  are  never  permanent  as 
with  masonry  or  concrete  linings.  Finally,  silting  a  canal 
is  often  recommended.  Clay  or  clayey  materials,  thrown 
into  the  water  at  various  places,  settle  wherever  the  grade 


FIG.  108.  Wooden  stave  pipe  carrying  irrigation  water. 


is  not  too  steep.  Afterwards,  the  silt  deposits  are  puddled 
by  the  chain  puddler.  This  is  a  very  cheap  and  often  an 
effective  method  of  preventing  seepage.  (Figs.  106,  107.) 
In  California,  whole  canals  have  been  lined  with  cement 
concrete,  and  the  definite  attempt  to  reduce  seepage  by 
first-class  canal  linings  has  become  established.  In  other 
states,  also,  large  canals  are  rapidly  being  lined.  One  of 


OVER-IRRIGATION  AND  ALKALI 


370 


the  most  notable  is  the  main  canal  of  the  Davis  and  Weber 
Counties  Canal  Company  of  Utah,  which  is  lined  with 


FIG.  109.  Lateral  lined  witn  concrete. 


cement  for  10  miles.  The  work,  authorized  by  farmers 
owning  the  canal,  was  done  under  the  direction  of  some 
of  the  best  engineers  of  the  country. 


OVER-IRRIGATION  AND  ALKALI  381 

Machines  and  molds  for  lining  farm  ditches  are  on  the 
market  and  may  be  obtained  at  relatively  small  cost. 
Pipes  are  often  most  desirable  for  the  smaller  ditches, 
since  they  eliminate  direct  loss  by  evaporation,  and  also 
the  growth  of  grass  or  algae  near  the  ditch  banks.  Smith 
has  shown  that  tile  may  be  made  of  cement  at  prices  so 
low  as  to  make  the  method  available  for  the  farm  irri- 
gation system.  The  good  irrigation  farmer  should  make 
the  ditches  under  his  control  as  impervious  as  is  possible. 

227.  The  economical  use  of  water — a  remedy. — The 
common  custom  of  allowing  water  to  run  hi  irrigation 
canals  during  the  whole  year,  when  it  is  really  needed 
only  a  few  months  of  the  year,  is  responsible  for  much 
seepage   and  positive   injury  to   the   lower-lying  lands. 
Water,  whether  taken  from  reservoir  or  river,  should  be 
allowed  in  the  canals  only  during  the  seasons  of  the  year 
of  actual  use.    Moreover,  on  the  farm,  it  should  be  used 
economically,   in   harmony  with   the  principles  already 
elaborated  in  this  volume.    By  the  more  economical  use 
of  water  in  these  two  directions  the  danger  of  water-logging 
will  be  greatly  reduced. 

228.  Drainage — the  final  remedy. — Even  in  the  arid 
region,  where  no  irrigation  is  practised,  there  will  be  some 
low-lying  wet  lands  resulting  from  the  natural  rainfall 
seeping  through  the  soil   from  the   highlands  and  the 
river  beds.    When  irrigation  is  established  and  practised, 
even  under  the  best  conditions,  the  area  of  wet  land  will 
be  somewhat  larger  than  it  was  before.    Naturally,  the 
best  and  final  remedy  for  this  condition  is  underdrainage. 
Underdrainage  has  been  well   tried  out  during  the  last 
hundred  years  in  Europe  and  in  the  eastern  United  States, 
and  has  been  found  to  be  a  great  and  helpful  factor  in 
making  agriculture  successful.    In  spite  of  the  apparent 


382 


IRRIGATION  PRACTICE 


paradox,  underdrainage  on  a  small  scale  must  be  a 
necessary  complement  of  irrigation.  The  sooner,  there- 
fore, that  underdrainage  is  established,  in  places  where  it 
is  necessary,  the  better  it  will  be  for  the  development  of 
the  irrigated  region.  The  low-lying,  water-logged  lands 
are  fertile,  and,  when  drained,  require  very  little  irri- 
gation. Many  excellent  experiments  have  been  made  on 


FIG.  111.  Pumping  plant.     (Lifts  water  37  feet  and 
irrigates  70  acres.    (Montana.) 

the  underdrainage  of  lands  in  the  irrigated  region,  and 
the  practice  has  been  found  to  be  wholly  successful  and 
in  cost  to  be  well  within  the  farmer's  reach. 

The  methods  for  underdrainage  under  irrigated  con- 
ditions are  only  slightly  different  for  those  prevailing 
under  humid  conditions.  Usually  an  upper  main  drain  is 
constructed,  transverse  to  the  flow  from  the  upper  canal, 
so  as  to  intercept  the  water  seeping  from  above.  (See 
Fig.  112.)  Where  the  subsoil  rests  on  a  hardpan,  blasting 


OVER-IRRIGATION  AND  ALKALI 


383 


the  impervious  layer  is  often  sufficient  to  improve  the 
drainage  and  to  send  the  obnoxious  standing  water  down- 
ward. It  has  also  been  proposed  that  water-logged  lands 
may  be  drained  by  pumping,  the  pumped  water  to  be 
lifted  to  reclaim  lands  yet  without  water.  Drainage  water 
of  the  right  composition,  that  is,  free  from  alkali,  can 
well  be  so  used,  especially  in  view  of  the  fact  that  the 
next  great  development  in  irrigation,  so  far  as  sources  of 
water  are  concerned,  will  be  the  use  of  subsoil  water  by 
pumping.  In  Europe,  the  practice  of  pumping  water  for 
the  purpose  of  reliev- 
ing the  land  from  ex- 
cessive moisture  and 
of  using  the  pumped 
water,  prevails  largely. 

Without  question, 
underdrainage  will 
become  an  established 
practice  in  the  irriga- 
tion region  as  it  is  in 
the  humid  region. 
The  excellent  drainage  investigations  of  the  Office  of 
Experiment  Stations  of  the  United  States  Department 
of  Agriculture  have  collected  a  great  deal  of  information 
concerning  the  right  methods  of  draining  irrigated  lands. 

229.  Alkali  defined. — Soluble  substances  are  being 
continuously  formed  in  all  soils  from  the  progressive 
decomposition  of  the  soil  particles.  Under  high  rainfall 
most  of  these  soluble  materials  are  washed  into  the  country 
drainage,  and  finally  into  the  ocean.  It  has  been  suggested 
that  the  salinity  of  the  ocean  is  at  least  in  part  due  to  the 
accumulation  of  salts  lost  by  soils.  Under  low  rainfall, 
which  penetrates  only  a  few  feet  of  soil,  the  soluble 


FIG.  112.  Drainage  of  irrigated  lands  by  inter- 
cepting drains. 


384  IRRIGATION  PRACTICE 

constituents  remain  in  the  soil  and  accumulate  as  the 
years  go  by.  This  is  one  of  the  characteristic  differences 
between  the  soils  of  arid  and  humid  regions.  These 
accumulations  often  become  so  large  as  to  be  injurious, 
and  then  are  called  alkali.  Alkali  means  the  water-soluble 
materials  in  the  soil,  especially  when  the  quantity  is  so 
large  as  to  be  injurious  to  plant-growth. 

Much  alkali  is  of  early  geological  origin.  In  early 
geological  times,  as  now,  large  accumulations  of  soluble 
soil  materials  occurred  in  lakes  similar  to  the  Great  Salt 
Lake  or  the  Dead  Sea.  When  these  prehistoric  interior 
lakes  dried  up,  there  were  left  behind  great  deposits  of  the 
salts  held  in  full  or  partial  solution  in  the  lake  water.  In 
time  these  layers  of  saline  materials  were  covered  by  silt 
and  other  materials  derived  from  soils,  and  thus  conserved 
until  the  present  day.  When  such  lands  are  irrigated  the 
water  dissolves  the  soluble  salts  which  may  become  very 
injurious. 

Ordinarily,  alkali  appears  as  an  incrustation  on  the 
soil  surface,  even  on  native  soils,  where  conditions  are 
favorable  to  the  accumulation  of  soluble  matter.  As  often, 
however,  alkali  does  not  appear  as  an  incrustation,  but 
is  held  in  the  concentrated  soil  solution,  with  equally 
injurious  effects. 

230.  Seepage  and  alkali. — Soils  tend,  naturally,  to 
retain  their  soluble  matters,  especially  those  of  value  in 
plant-growth;  but,  when  a  continuous  excess  of  water 
passes  through  the  soil,  the  soluble  substances  are  given 
up  and  pass  into  the  country  drainage.  When  such  seepage 
water,  heavily  charged  with  salts,  appears  in  some  low- 
lying  place  and  is  evaporated,  the  alkali  is  left  behind, 
either  on  the  surface  or  in  the  remaining  soil  water  itself. 
In  either  case,  the  soil  becomes  increasingly  less  suitable 


OVER-IRRIGATION  AND  ALKALI  385 

for  plant-production.  By  over-irrigation,  water  is  lost, 
plant-food  is  lost,  the  upper  lands  are  impoverished  and 
the  lower  lands  made  useless. 

The  whole  process  is  well  illustrated  on  a  large  scale 
by  the  inland  salt  lakes,  found  in  abundance  over  the 
arid  region,  such  as  the  Great  Salt  Lake.  This  lake  is  fed 
by  the  seepage  from  the  neighboring  territory,  and 
by  rivers  flowing  directly  into  it.  It  has  no  outlet. 
Water  is  lost  from  the  lake  chiefly  by  evaporation, 
and  the  soluble  substances  carried  by  the  water  entering 
the  lake  are  accumulated  in  the  lake  water.  As  a  result, 
the  water  has  become  so  saturated  that  crystallization  is 
going  on.  On  a  smaller  scale,  in  every  valley  bottom  with 
poor  drainage,  the  process  is  being  repeated.  Large 
areas  have  thus  been  and  are  being  made  alkaline. 

231.  Upward  leaching. — Another  phase  of  the  alkali 
question  does  not  concern  itself  with  seepage.  Arid 
soils  are  rich  in  soluble  matters,  which,  when  evenly 
distributed  throughout  the  soil,  are  advantageous  hi 
plant-growth.  If  by  any  chance  the  soluble  substances  of 
the  upper  6  to  10  feet  of  the  soil  are  partly  concentrated 
near  the  surface,  plant  injury  is  almost  sure  to  follow. 
Such  concentration  frequently  occurs  under  irrigation. 
Water,  added  to  the  soil  in  moderation  moves  downward 
only  a  few  feet,  but  in  its  descent  dissolves  some  of  the 
water-soluble  soil  constituents.  By  transpiration  and 
evaporation  the  water  thus  added  moves  upward  and 
carries  with  it  the  substances  dissolved  in  its  descent.  At 
the  soil  surface,  the  water  evaporates  and  the  salts  are  left 
behind.  As  this  is  continued,  the  soluble  soil  constituents 
tend  to  accumulate  at  or  near  the  surface.  This  process 
has  been  named  upward  leaching.  It  is  a  condition  that 
need  not  cause  permanent  injury,  for  it  may  be  controlled. 


386 


IRRIGATION  PRACTICE 


The  process  has  gone  on  in  nature  for  many  ages;  the 
salts  have  each  year  been  washed  down  to  a  depth  ordi- 
narily reached  by  the  rainfall  and  returned  to  the  surface 
during  the  warmer  season.  Arid  soils  are  often  underlaid 
at  a  certain  depth  by  layers  of  salts  which  indicate  the 


•UOOO 

FIG.  113.  Structure  of  an  alkali  spot. 

annual  penetration  of  the  rainfall  throughout  the  ages 
before  man  began  to  cultivate  the  soil.    (Fig.  113.) 

Upward  leaching  may  be  prevented  by  preventing 
evaporation  from  the  soil  surface.  The  tillage  methods 
recommended  for  the  conservation  of  water  are  those 
that  will  prevent  the  accumulation  of  alkali  at  the  soil 
surface. 


OVER-IRRIGATION  AND  ALKALI  387 

232.  Use  of  saline  water. — Another  source  of  alkali  is 
the  use  of  water  charged  with  large  quantities  of  soluble 
salts.  As  shown  in  Chapter  V,  all  natural  waters  contain 
certain  quantities  of  dissolved  substances.  Only  when  the 
proportion  of  such  soluble  salts  is  too  large  does  there 
appear  to  be  any  danger  hi  the  use  of  such  waters.  In 
fact,  saline  waters  have  usually  been  undervalued  for 
purposes  of  irrigation. 

Plants  can  tolerate  large  quantities  of  soluble  salts  hi 
irrigation  water  providing  they  are  of  the  right  mixture. 
Thus  Kearney  and  Cameron  found  that  seventy  parts  of 
magnesium  sulphate  in  1,000,000  parts  of  water  repre- 
sented the  highest  concentration  hi  which  plant-roots 
could  survive;  yet,  hi  the  presence  of  a  concentrated 
solution  of  calcium  sulfate,  33,600  parts  of  magnesium 
sulphate  in  1,000,000  parts  of  water  could  be  tolerated. 
Gypsum  and  common  salt  are  both  antidotes  for  mag- 
nesium sulfate;  magnesium  carbonate  is  an  antidote  for 
sodium  carbonate  and  sodium  chloride,  raising  their  limit 
two  to  four  times;  lime  is  an  antidote  for  magnesium  and 
sodium,  hi  the  form  of  sulfates,  carbonates  or  chlorides, 
raising  the  limit  of  these  dangerous  salts  hundreds  of 
times.  Kearney  found  that  the  native  irrigationists  of 
northern  Africa  raised  successfully  many  of  the  ordinary 
crops  with  water  containing  8,000  parts  of  soluble  salts 
for  each  1,000,000  parts  of  water.  Hilgard,  as  a  result 
of  his  long  life  of  experimentation  on  such  subjects,  holds 
that  from  1,200  to  1,700  parts  of  soluble  matters  hi  each 
1,000,000  parts  of  water  represent  the  highest  limit  of 
endurance  for  ordinary  plants.  This,  however,  is  much 
lower  than  that  observed  by  Kearney  hi  northern  Africa, 
or  observed  by  other  students  hi  other  parts  of  the  world. 
The  concentration  of  water  that  may  be  used  for  irrigation 


388  IRRIGATION  PRACTICE 

purposes  depends  primarily  upon  the  proportions  of  the 
salts  in  the  water.  The  poisonous  action  of  irrigation 
water  is  not  the  sum  of  the  poisonous  actions  of  its  various 
constituents;  for,  as  observed,  the  effect  of  any  compound 
is  qualified  by  the  presence  of  other  compounds.  The  whole 
subject  is  in  a  confused  state  and  needs  extensive  in- 
vestigation. 

The  real  danger  in  the  use  of  saline  waters  for  irriga- 
tion, whether  they  contain  1,000  or  8,000  parts  of  soluble 
matter  to  1,000,000  parts  of  water,  is  in  the  residue  of 
salts  from  the  evaporated  matter.  For  example,  if  an 
irrigation  water  contains  1,000  parts  of  soluble  matter 
in  each  1,000,000  parts  of  water,  and  if  18  inches  of  this 
water  are  used  over  an  acre  each  year,  4,000  pounds  of 
alkali  an  acre  are  added  each  year.  As  this  is  repeated 
year  after  year,  the  accumulation  of  salts  becomes  so 
great  as  to  render  the  land  unfit  for  farming.  To  over- 
come this  difficulty  it  is  necessary,  when  saline  waters  are 
employed  in  irrigation,  to  reverse  the  usual  rule,  and  to 
use  quantities  of  water  so  large  that  drainage  is  assured. 
The  excess  of  salt  is  then  washed  into  the  country  drain- 
age, and  alkali  accumulations  are  prevented.  Such  hand- 
ling of  saline  waters  is,  however,  dangerous  in  that  the 
excess  of  water,  heavily  alkaline,  may  appear  on  the 
lower  lands,  there  to  cause  injury.  Before  saline  waters 
are  used  for  irrigation,  they  should  be  investigated  care- 
fully as  to  their  composition  and  their  probable  effect 
on  the  land. 

233.  Alkali  deposits. — The  great  deposits  of  alkali  or 
alkali  impregnated  soils  and  rocks  common  to  arid 
countries  are  another  source  of  alkali.  These  deposits, 
yet  to  be  studied  exhaustively,  are  associated  with  the 
geological  history  of  the  country.  In  early  geological 


OVER-IRRIGATION  AND  ALKALI 


389 


days,  salt  lakes,  similar  to  the  Great  Salt  Lake,  were  no 
doubt  formed,  which  were  dried  by  the  changing  climate, 
leaving  great  masses  of  salt,  that  were  later  covered  by 
washings  from  the  hills.  In  other  cases,  silt  and  other 


Fia.  114.  Quaternary  Lakes  of  the  Great  Basin.    Sources  of  alkali  deposits. 

soils  of  early  geological  days  were  deposited  in  the  presence 
of  salt  or  brackish  water.  These  in  time  became  hardened 
into  rocks.  Consequently,  over  much  of  western  America 
there  are  great  exposures  of  shales  and  sandstones  con- 
taining large  percentages  of  water-soluble  substances. 


390  IRRIGATION  PRACTICE 

On  the  soils  derived  from  many  of  these  deposits,  plant- 
growth  is  difficult  or  impossible,  and  they  are  therefore 
easily  recognized. 

Water  passing  through  these  alkali  deposits  of  early 
times  and  dissolving  the  salts,  carries  alkali  to  otherwise 
alkali-free  sections.  This  is  a  chief  source  of  alkali,  next 
in  importance  to  over-irrigation,  although  it  has  been 
largely  overlooked  by  students  of  alkali.  Knight  and 
Slosson,  of  Wyoming,  have  shown  that  great  numbers  of 
such  deposits  occur  in  Wyoming;  other  students  of 
western  conditions  have  discovered  similar  deposits  in 
various  districts;  and  Stewart  and  Peterson,  of  Utah, 
have  recently  confirmed  the  wide  distribution  of  such 
alkali  deposits.  Once  the  existence  of  such  deposits  is 
recognized  in  the  neighborhood,  precautions  against  them 
may  be  taken,  and  they  need  not  then  be  a  menace. 
(Fig.  114.) 

234.  Kinds  of  alkali. — Since  alkali  is  simply  the 
soluble  matter  of  soils  accumulated  to  an  injurious  degree, 
it  follows  that  alkali  may  contain  any  or  all  of  the  con- 
stituents of  rocks  and  soils.  The  numerous  existing  analy- 
ses show  that  in  alkali  there  is  a  preponderance  of  the 
bases,  sodium,  calcium  and  magnesium,  combined  with 
hydrochloric,  sulfuric,  carbonic  and  nitric  acids.  In 
other  words,  the  chlorides,  sulfates,  carbonates  and 
nitrates  of  sodium,  calcium  and  magnesium  are  the  chief 
constituents  of  ordinary  alkali.  In  addition  to  these 
dominant  constituents  there  are  a  great  many  others,  as 
potassium  salts,  phosphates  and  other  indispensable 
plant-foods.  Alkali  may  be  said  to  be  the  cream  of  soil 
fertility,  so  concentrated  as  to  cause  plant  indigestion. 
The  following  table  gives  partial  analyses  of  four  samples 
of  alkali  crust: 


OVER-IRRIGATION  AND  ALKALI 


391 


PERCENTAGE  COMPOSITION  OF  ALKALI  CRUSTS 


New 
Mexico 

Wyoming 

Utah 

Colorado 

Utah 

Sodium  carbonate  (sal- 
soda)  

Trace 

Trace 

2.0 

Sodium  chloride  (common 
salt)  .  .  . 

3.2 

1.9 

1.4 

88.6 

Sodium  sulfate  (Glau- 
ber's salt)  

70.4 

39.7 

3.2 

Sodium  nitrate  (niter) 
Magnesium  sulfate   (Ep- 
som salts) 

Trace 
3  2 

Trace 
42.4 

Trace 

40.8 

•    • 

Calcium  sulfate  (gyp- 
sum) .... 

11.8 

3.6 

90.3 

30.5 

In  the  first  sample  from  New  Mexico,  sodium  sulfate, 
or  Glauber's  salt,  predominates;  in  the  second,  from 
Wyoming,  magnesium  sulfate,  or  Epsom  salts,  is  most 
prominent;  hi  the  third,  from  Utah,  calcium  sulfate,  or 
gypsum,  predominates;  in  the  fourth,  from  Colorado, 
sodium  nitrate,  or  niter,  predominates,  and  hi  the  fifth, 
from  Utah,  sodium  chloride,  or  common  salt,  predom- 
inates. 

Between  the  extreme  compositions  shown  hi  the  above 
table,  all  possible  variations  occur.  It  is  impossible  to 
lay  down  any  rule  for  the  composition  of  alkali,  unless 
the  source  is  known.  The  following,  analysis  of  a  Cali- 
fornia sample  also  shows  the  gpmplex  composition  of 
alkali : 

Potassium  sulfate 3.95 

Sodium  sulfate      25.28 

Sodium  nitrate      19.78 

Sodium  carbonate 32.58 

Sodium  chloride 14.75 

Sodium  phosphate 2.25 

Ammonium  carbonate.    .  1.41 


Total .    100.00 


392 


IRRIGATION  PRACTICE 


Ordinarily,  alkali  is  classified  as  white,  black  or  brown. 
Black  alkali  appears  as  a  black,  shiny  mass,  or  as  black 
spots,  over  the  soil.  White  alkali  has  a  clean,  white  appear- 
ance like  that  of  salt.  Experience  has  demonstrated  that 
black  is  far  more  injurious  than  white  alkali,  for  it  is 
corrosive  and  girdles  the  tissues  of  the  plant  near  the 
soil  surface  and  thus  destroys  the  plant  itself.  White 
alkali  is  relatively  harmless,  and  injures  plants  only  as  it 

is  present  in  too 
large  an  abun- 
dance. Black  or 
brown  alkali  is 
composed  chiefly 
of  the  carbonate 
or  nitrate  of 
sodium,  with 
perhaps  some 
common  salt. 
The  carbonate  dissolves  the  plant  tissues  with  the  for- 
mation of  a  black  mass;  it  moreover  destroys  the  tilth  of 
the  soil  by  destroying  its  structure.  The  nitrate  forms 
brown  spots;  it  also  makes  soils  mushy;  but,  when  the 
soils  containing  nitrates  dry  out,  a  very  characteristic 
crumbly  soil  results.  The  white  alkali  is  composed  of 
the  sulfates  and  chlorides  of  sodium,  calcium  and 
magnesium. 

235.  Tolerance  for  alkali. — The  tolerance  for  alkali  of 
plants  depends  on  five  factors:  (1)  the  main  salt,  (2) 
the  concentration,  (3)  the  associated  salt,  (4)  the  age  of 
the  plant,  and  (5)  the  plant  itself.  Kearney  and  Cameron, 
experimenting  with  seedlings  of  various  plants,  have 
shown  that  various  salts  affect  growth  variously.  Sodium 
carbonate  is  the  most  injurious  constituent  of  alkali, 


1  2  3  4 

FIG.  115.  Effect  of  a  strong  solution  of  potassium 
nitrate  on  protoplasm. 


OVER-IRRIGATION  AND  ALKALI 


393 


followed  by  sodium  chloride,  followed  by  sodium  sulfate, 
followed  by  magnesium  sulfate.  This  is  the  general  order 
of  tolerance  of  these  four  important  salts,  frequent  con- 
stituents of  alkali. 

The  injury  from  each  salt  depends  upon  the  mixtures 
of  salts  hi  the  alkali.  The  action  of  magnesium  sulfate 
is  almost  wholly  destroyed,  if  there  is  mixed  with  it  a 
quantity  of  calcium  sulfate.  In  fact,  calcium  sulfate  is 
the  great  neutralizer  of  the  dangerous  substances  of 


FIG.  116.   Vegetation  on  alkali  lands.   California. 

ordinary  alkali.  The  salts  found  in  alkali  do  not  show 
any  specific  effect  upon  the  wilting  coefficient.  Any 
of  the  alkali  salts,  present  in  large  quantity,  tends  to 
increase  the  water-cost  of  dry  matter.  Evaporation  from 
alkali  soils  is  always  reduced.  In  general,  while  alkali  tends 
to  reduce  the  direct  evaporation  from  the  soil,  it  also  tends 
to  increase  the  water-cost  of  dry  matter. 

The  concentration  of  alkali  hi  the  soil  that  will  injure 
plants  has  not  been  finally  determined.  Most  work  on  the 
subject  has  been  done  by  Hilgard  and  Loughridge  of 
the  University  of  California.  Loughridge  has  tabulated 
the  highest  quantity  of  alkali  salts  endured  by  various 


394 


IRRIGATION  PRACTICE 


crops,  as  based  upon  many  years  of  observation  at  the 
California  stations.  In  the  following  table  will  be  found 
the  information  given  by  Loughridge,  adapted  slightly: 

HIGHEST  QUANTITY  OF  ALKALI  SALTS  ENDURED  BY  VARIOUS  CROPS 
Fruit  Trees 


Per  cent  of 
sodium  sulfate  (Glau- 
ber's salt)  in  soil 

Per  cent  of  sodium 
chloride  (common  salt) 
in  soil 

Per  cent  of 
sodium  carbonate  (sal- 
soda)  in  soil 

Grapes  0.25 

Grapes.  .  .  . 
Olives  .... 

0.062 
•  '  '  VO.05-0.01 

Grapes  } 

Olives.  .  .           .      )  n  on    n  -i  c 

8ifvnJes:::  ::W-o.ooi 

Pears  J 
Almonds  
Prunes  O.OC10-C.OOO, 

Figs  ..:::::  }°-2(MU5 

Oranges  .  .  . 
Almonds.  . 
Mulberry.  . 
Pears  

Almonds  ) 
Oranges  >•  0.15-0.10 
Pears  ) 

Apples  .            ^ 

Apples  .  .  . 

Figs 

Peaches  V,/-)  inn  nc 

Prunes  .... 

Peaches  
Apples  
Apricots                0  0005-0  000 

Prunes  I    ' 
Apricots.           / 

Peaches  
Apricots 

0.01-0.005 

Lemons  I  n  no^ 
Mulberry  f0'025 

Lemons.  .  . 

Lemons  
Mulberry  

Figs  

Small  Cultures 


Per  cent  of 
sodium  sulfate  (Glau- 
ber's salt)  in  soil 

Per  cent  of  sodium 
chloride  (common  salt) 
in  soil 

Per  cent  of 
sodium  carbonate  (sal- 
soda)  in  soil 

Saltbush  
Alfalfa  (old).. 
Hairy  vetch  .  .  -\ 
Sorghum  
Sugar  beets  .  . 
Sunflower.  .  .  . 
Radish  
Salt-grass  
Artichoke  
Carrot  ^ 
Gluten  wheat  .  ' 
Wheat  j 
Barley  ) 
Goat's  rue  
Alfalfa 
(young)  
Rye                  1 

0.75-0.50 
0.50-0.25 

^0.25-0.10 
•0.10-0.05 

0.05-0.01 

Salt-grass  0.43 

Salt-grass  0.84 

Modiola  0.25 
Saltbush  } 

ft8±£:  ::}*««* 

Celery  ) 
Onions  ' 
Potatoes  
Sunflower  
Barley 

Saltbush  
Barley  ' 
Bur  clover.  ... 
Sorghum  
Radish  , 
Modiola  
Sugar  beets  .  .  . 
Gluten  wheat  . 
Artichoke  
Lupine  
Hairy  vetch..  . 
Alfalfa  
Grasses  
Kafir  corn  .    . 
Sweet  corn    . 
Sunflower.  .  .  . 
Wheat  \ 
Carrots  1 
Rye  j 
Goat's  rue.  .  .  ./ 
White  melilot. 
Canaigre  , 
Salt-grass  ' 

.0.12 
>0.075-0.050 

0.050-0.025 
-0.025-0.010 

,0.010-0.005 
0.005-0.001 

Hairy  vetch  .  .  \>  0.05-0.01 
Lupine  
Carrot  
Radish  
Rye  

Artichoke  ^ 

Grasses  / 
White  melilot  .  1 
Goat's  rue  ....  V  0.0025-0.0005 
Canaigre  ) 

Canaigre  
Rye-grass 
Modiola  
Bur  clover  .  .  . 
Lupine  
White  melilot  . 
Celery  ) 

OVER-IRRIGATION  AND  ALKALI  395 

For  fruit  trees,  the  tolerance  of  Glauber  salts  varies 
from  0.25  to  0.025  of  1  per  cent;  of  common  salt  from 
0.062  to  0.005  of  1  per  cent;  of  sal-soda  from  0.005  to 
0.0001  of  1  per  cent.  For  the  small  cultures,  tolerance  of 
Glauber's  salt,  as  of  salt  and  sal-soda,  is  increased  con- 
siderably. However,  the  variation  for  various  crops  in 
the  table  is  so  great  as  to  make  it  practically  impossible 
to  lay  down  any  definite  rules  that  may  be  generally  used 
in  agriculture.  Loughridge  concludes  that,  in  general,  for 
fruit  trees,  the  maximum  tolerance  of  alkali  in  the  soil 
ranges  from  0.28  per  cent  to  0.04  per  cent;  for  small 
cultures,  excluding  the  salt  bushes,  from  1.0  per  cent  to 
0.06  per  cent. 

The  experience  of  the  Bureau  of  Soils  is  perhaps  the 
best  for  formulating  limits  of  the  tolerance  of  plants  for 
alkali.  The  staff  of  the  Bureau  of  Soils  has  investigated 
practically  every  important  alkali  area  of  the  United  States. 
They  have  had  ample  opportunity  to  correlate  the 
growth  on  the  soil  with  the  alkali  content.  It  has  been 
found  that  on  land  containing,  to  a  depth  of  6  feet, 
up  to  0.2  per  cent  of  total  alkali,  none  of  the  common 
crops  are  injured,  unless  carbonates  greatly  predominate, 
or  unless  most  of  the  salt  is  concentrated  in  the  upper 
part  of  the  first  foot.  On  land  containing  from  0.2  per 
cent  to  0.4  of  total  alkali,  or  from  0.05  to  0.1  per  cent  of 
black  alkali,  or  0.5  per  cent  of  sodium  chloride,  or  1  per 
cent  of  sodium  sulfate,  all  but  the  most  sensitive  crops 
will  grow.  Near  the  higher  limits,  all  but  the  most  resis- 
tant crops  show  signs  of  distress.  A  grade  of  land  contain- 
ing from  .4  to  .6  per  cent  of  total  alkali  and  from  .1  to  .2 
of  black  alkali  contains  a  little  too  much  for  common 
crops.  Pastures  usually  grow  on  such  land.  Where  the 
land  contains  from  .6  to  1  per  cent  of  total  alkali  it  is 


396  IRRIGATION  PRACTICE 

almost  worthless  for  general  or  fruit  farming.  In  spite, 
however,  of  these  well-established  limits,  it  is  known  that 
even  with  3  per  cent  of  alkali  in  the  upper  6  feet,  crops 
may  occasionally  be  grown  successfully.  Much  depends, 
as  already  said,  upon  the  crop,  the  nature  of  the  alkali, 
the  nature  of  the  soil,  methods  of  irrigation,  and  tillage. 


FIG.  117.  Alkali  spots  on  irrigated  pasture. 

The  crop  itself  determines,  fundamentally,  the  tolerance 
for  alkali.  Certain  fruits  and  small  crops  endure  large 
quantities  of  alkali,  while  others  are  very  sensitive  to  it. 
When  properly  cultivated,  kafir  corn,  sorghum,  sugar 
beets,  and  barley  are  excellent  alkali-resistant  crops. 
The  date  palm,  in  its  resistance  to  alkali,  stands  at  the 
very  head  of  cultivated  crops.  However,  the  area  over 
which  this  plant  may  be  grown  at  present  is  relatively 
small. 


OVER-IRRIGATION  AND  ALKALI  397 

The  age  of  the  crop  also  determines  largely  the  tol- 
erance of  alkali.  Germinating  crops  can  stand  only  small 
quantities  of  alkali;  but  as  they  become  older  and  the  root- 
system  better  established  the  tolerance  increases.  There- 
fore, it  is  advisable  to  wash  the  alkali  far  down  into  the 
subsoil  at  the  time  of  seeding,  so  that  germination  and 
first  growth  may  occur  without  hindrance.  The  quality 
of  crops  is  often  reduced  by  the  presence  of  alkali. 
Headden  found  that  the  quality  of  beets  was  largely 
interfered  with  by  the  presence  of  nitrates  in  the  soil. 

All  in  all,  the  subject  of  the  tolerance  of  plants  for 
alkali  is  in  considerable  confusion.  This  exceedingly 
difficult  subject  needs  to  be  worked  over,  with  new 
experiments  and  devices  before  the  last  word  concerning 
it  can  be  spoken. 

236.  Cropping  against  alkali. — Apparently  the  sim- 
plest method  of  utilizing  alkali  lands  is  to  grow  upon 
them  alkali-resistant  plants.  Many  native  plants  thrive 
on  alkali  lands,  and  are  relatively  sure  indicators  of  alkali 
conditions.  Greasewood,  shad-scale,  salt-weeds  and  salt- 
bushes  thrive  best  on  lands  that  are  fairly  rich  in  alkali. 
While  these  plants  usually  grow  on  alkali  soils  they  often 
do  well  on  alkali-free  soils,  and  are  not  therefore  invariable 
indicators  of  alkali.  Unfortunately,  most  of  the  native 
alkali-resistant  plants  have  little  agricultural  value.  They 
are  usually  unpalatable  and  of  low  digestibility  and 
feeding  value.  There  are  a  number  of  cultivated  plants 
that  also  endure  alkali.  Among  these  is  the  Australian 
salt-bush,  tried  out  in  California,  which  yields  well  and 
makes  a  fairly  palatable  forage.  Sweet  clover,  which 
is  almost  a  weed  hi  many  localities,  grows  remarkably 
well  on  certain  classes  of  alkali  land,  and,  if  cut  early, 
forms  a  palatable  stock-feed.  Lucern  once  started  on 


398  IRRIGATION  PRACTICE 

alkali  land,  does  fairly  well,  as  do  also  sugar  beets,  sorghum, 
kafir  corn,  rye,  the  date  palm,  grape-vines  and  many 
other  crops  which  yield  annual  crops  of  fair  size  in  the 
presence  of  relatively  large  quantities  of  alkali. 

The  theory  of  reclaiming  alkali  lands  by  cropping  is 
that  each  crop  absorbs  from  the  soil  considerable  quan- 
tities of  alkali,  and  as  cropping  is  continued  year  after 
year,  there  is  diminution  in  the  alkali  content  of  the  soil 
corresponding  to  the  quantities  removed  by  the  crops. 
The  Australian  salt-bush,  containing  about  20  per  cent 
of  ash,  may  yield  five  tons  an  acre,  which  means  each 
crop  removes  from  the  soil  about  one  ton  of  alkali.  This, 
continued  for  several  years,  would  tend  to  make  an  alkali 
soil  better  capable  of  producing  ordinary  crops. 

On  alkali  soils,  deep-rooted  plants  do  better  than 
shallow-rooted  plants,  and  leafy  plants  do  better  than 
those  giving  less  shade.  Legumes  do  not  resist  alkali  well, 
while  the  sunflower  family  does  exceedingly  well  in  the 
presence  of  alkali.  The  fiber  plants,  such  as  flax,  are 
sensitive  to  alkali.  Much  information  is  yet  needed  con- 
cerning alkali-resistant  plants;  the  conditions  under 
which  they  thrive  best,  and  the  degree  to  which  they  are 
able  to  remove  alkali.  Much  new  work  can  profitably  be 
done  on  this  branch  of  the  subject  of  alkali. 

237.  Chemical  treatment  for  alkali. — The  suggestion 
has  been  made  repeatedly  that  something  might  be  added 
to  the  soil  to  neutralize  alkali.  The  chemical  nature  of 
the  constituents  of  alkali  makes  it  difficult  to  make  them 
insoluble  or  to  change  them  into  something  less  obnoxious. 
The  conclusion  has  been  reached,  after  much  experi- 
mentation, that  only  sodium  carbonate  may  be  corrected, 
practically,  by  chemical  treatment.  Hilgard  demon- 
strated many  years  ago,  on  the  California  experimental 


OVER-IRRIGATION  AND  ALKALI  399 

farms,  that  calcium  sulfate,  or  gypsum,  added  to  a  soil 
containing  sodium  carbonate,  changed  the  carbonate  to 
a  sulfate;  that  is,  gypsum  changed  black  alkali  to  white 
alkali.  Twice  as  much  gypsum  as  there  is  sodium  car- 
bonate in  the  soil,  should  in  time  be  worked  into  the  soil 
thoroughly.  To  add  200  to  400  pounds  of  gypsum  an 
acre  annually,  is  better  than  to  attempt  to  add  the  full 
quantity  all  at  once.  After  each  treatment  the  soil  should 
be  irrigated.  This  is  an  excellent  corrective  for  black 
alkali;  and  it  is,  indeed,  the  only  known  chemical  cor- 
rective for  alkali. 

238.  Scraping  the  surface. — Another  method  of  com- 
bating alkali  is  to  allow  evaporation  to  go  on  until  the 
alkali  has  crusted  the  soil  surface,  and  then  to  scrape  off 
this  crust  and  to  remove  it  permanently  from  the  soil.  By 
this  method,  hundreds  of  pounds  of  alkali  per  acre  may 
be  removed  from  the  soil;  but  not  enough  is  carried  off 
really  to  improve  the  soil,  and  the  labor  involved  is  so 
large  as  to  make  the  whole  process  of  doubtful  value. 

239.  Tillage  against  alkali. — Alkali  is  most  injurious 
if  concentrated  near  the  surface.    If  distributed  evenly 
throughout  the  soil  relatively  large  quantities  of  alkali 
may  be  endured  by  plants.  This  condition  may  be  secured, 
measurably,  by  reducing  evaporation  and  thereby  pre- 
venting the  rise  of  alkali.   This  is  a  very  effective  method 
of  preventing  damage   from  alkali.    Orchards  seriously 
injured  by  alkali   have  frequently  been  restored  to   a 
profitable  condition  by  thorough  cultivation.    The  com- 
mon custom  is  to  plow  under  the  crust,  irrigate  thoroughly, 
and  follow  this  by  a  thorough  cultivation  as  often  as 
needs  be  throughout  the  season.   Alkali  lands  should  also 
be  cultivated  in  the  spring,  when  evaporation  is  likely  to 
go  on  rapidly. 


400  IRRIGATION  PRACTICE 

240.  Washing  out  alkali. — In  the  attempt  to  remove 
alkali,  lands  are  often  flooded  with  a  large  quantity  of 
water  flowing  under  a  high  head.    The  theory  has  been 
that  the  rapidly  moving  water  passing  over  the  soil  will 
dissolve  the  alkali  and  carry  it  off.    This,  however,  has 
been  found  to  be  ineffective,  for,  the  moment  the  water 
dissolves  the  alkali,  it  sinks  into  the  soil  and  only  the  pure 
water  runs  off  the  surface. 

A  better  method  is  to  apply  irrigations  so  large  that 
the  water  seeps  into  the  country  drainage.  When  this 
can  be  done  it  is  very  satisfactory,  but  only  on  naturally 
well-drained  lands,  or  on  open  soils,  can  it  be  made 
effective.  Occasionally,  the  soil  is  underlaid  by  a  hard- 
pan,  and  it  is  found  helpful  to  make  holes  through  this 
impervious  layer  to  connect  with  the  more  permeable  soil. 
In  any  case,  when  much  water  is  used  on  alkali  land,  irri- 
gation should  be  followed  by  careful  cultivation. 

241.  Underdrainage    the    final    remedy. — The    only 
really  satisfactory  treatment  for  alkali  is  one  that  removes 
the  alkali  permanently  from  the  soil.   This  is  accomplished 
best  by  underdrainage,  since  few  soils  permit  of  natural 
drainage. 

The  feasibility  of  underdrainage  has  been  demon- 
strated in  all  parts  of  the  world,  and  the  only  consider- 
ations, with  respect  to  alkali  lands,  are  the  cost  of  instal- 
lation and  the  disposition  of  the  drainage  water.  The  cost 
is  no  higher  in  irrigated  than  in  humid  regions;  and  irri- 
gated lands  are  fully  as  valuable  as  those  in  humid  regions. 
The  disposition  of  the  drainage  water  depends  on  local 
conditions,  and  must  be  carefully  determined  upon,  for 
the  drainage  from  alkali  lands  is  unfit  for  agricultural 
uses.  Drainage  from  such  lands  need  not,  however,  be 
continuously  great,  for  lands,  underdrained  for  the  re- 


OVER-IRRIGATION  AND  ALKALI  401 

moval  of  alkali,  are  not  necessarily  swampy;  on  the 
contrary,  they  may  be  perfectly  dry  in  their  natural 
condition. 

If  underdrainage  is  used  as  the  final  remedy  for  alkali, 
very  heavy  applications  of  water  must  be  applied  for 
some  time,  until  the  alkali  is  thoroughly  washed  out  and 
carried  off  through  the  drains.  This  is  a  dangerous 
procedure,  for  valuable  plant-foods  are  taken  out  with  the 
alkali.  The  washing  of  the  soil  should  be  stopped,  there- 
fore, as  soon  as  the  main  alkali  condition  has  been  cor- 
rected. 

The  possibility  of  removing  alkali  by  underdrainage 
has  been  well  demonstrated  by  the  Bureau  of  Soils  of  the 
United  States  Department  of  Agriculture.  The  pioneer 
experiment  was  made  on  land  located  west  of  Salt  Lake 
City,  toward  the  Great  Salt  Lake.  The  farm,  when 
located,  was  covered  with  a  glistening  coat  of  white 
alkali.  The  soils  of  the  district  are  generally  heavily 
impregnated  with  alkali,  chiefly  common  salt,  from  the 
concentrated  water  of  the  Great  Salt  Lake,  which  has 
either  overflowed  hi  the  past,  or  has  moved  through  the 
subsoil.  From  2J^  to  5  per  cent  of  alkali  was  found  in  the 
soil  at  the  time  the  experiments  began,  and  ground  water 
stood  about  4  feet  from  the  surface.  Tile  pipe  was  laid 
in  the  usual  manner,  at  a  cost  of  about  $16  an  acre.  In 
1903,  the  year  after  the  laying  of  the  tile,  the  land  was 
thoroughly  flooded,  and  from  August,  1904,  it  was  again 
flooded  thoroughly,  at  various  intervals,  until  1906,  when 
the  land  was  returned  hi  a  good  agricultural  condition  to 
the  owner.  Since  that  time  a  thrifty  crop  of  alfalfa  has 
grown  upon  it,  as  proof  that  the  alkali  condition  has  been 
permanently  corrected.  From  September,  1902,  to  Octo- 
ber, 1904,  the  water  added  was  equal  to  a  little  more 
z 


402  IRRIGATION  PRACTICE 

than  10  feet  in  depth  over  the  whole  area.  This  quantity 
of  water  carried  off  5,317  tons  of  salt,  and  reduced  the 
alkali  content  to  13  per  cent  of  what  it  was  at  the  beginning 
of  the  experiment.  Not  only  was  this  tract  of  40  acres 
reclaimed  by  this  treatment,  but  the  beneficial  effects  of 
the  drainage  were  felt  in  the  adjoining  fields. 

At  Fresno,  California,  where  the  predominating  type 
of  alkali  was  a  mixture  of  the  chloride  and  the  carbonate 
of  sodium,  a  hopelessly  alkaline  tract  was  restored  by  tile 
drainage  in  less  than  one  year  to  permanent  fertility.  At 
Billings,  Montana,  where  the  prevailing  type  of  alkali 
was  sodium  sulphate,  similar  reclamation  work  was 
accomplished  in  two  years.  These  three  experiments, 
at  Salt  Lake  City,  Fresno,  and  Billings,  representing  the 
three  chief  types  of  alkali,  demonstrate  the  feasibility  of 
reclaiming  alkali  lands  by  underdrainage,  provided  there 
is  a  sufficient  fall  of  the  land  and  a  suitable  outlet. 

Alkali  may  attack  and  injure  the  materials  of  which 
the  drains  are  made.  When  glazed  pipe  is  used,  the  danger 
is  small;  but  if  concrete  or  cement  pipe  is  laid,  the  danger 
is  large,  for  alkali  uniting  with  the  calcium  hydroxide 
of  the  cement  tends  to  disintegrate  concrete.  In  the  de- 
structive action  on  concrete,  sodium  sulfate  stands  first, 
followed  by  magnesium  sulfate  and  then  by  sodium 
carbonate.  Sodium  chloride  has  a  small  but  definitely 
injurious  effect. 

Alkali  lands  represent  only  a  small  proportion  of  the 
total  irrigated  area.  Cautious  irrigation  of  the  higher- 
lying  lands  will  prevent  the  increase  of  this  area,  and 
underdrainage  will  reduce  it  considerably.  With  our  pres- 
ent knowledge,  there  is  no  reason  why  the  "alkali  plague" 
should  be  feared.  Vigorous  measures  should  be  taken, 
however;  if  the  alkali  trouble  is  approaching. 


OVER-IRRIGATION  AND  ALKALI  403 

REFERENCES 

BONSTEEL,  JAY  A.     Marsh    and    Swamp    Lands.    United  States 

Department  of  Agriculture,  Bureau  of  Soils,  Circular  No.  69 

(1912). 
BROWN,  CHARLES  F.    Drainage  of  Irrigated  Lands.    United  States 

Department  of  Agriculture,  Farmers'  Bulletin  No.  371  (1909). 
BROWN,  CHARLES  F.,  and  HART,  R.  A.  The  Reclamation  of  Seeped 

and  Alkali  Lands.   Utah  Experiment  Station,  Bulletin  No.  Ill 

(1910). 
BURKE,  EDMUND,  and  PINCKNEY,  REUBEN  M.   The  Destruction  of 

Hydraulic  Cements  by  the  Action  of  Alkali  Salts.    Bulletin 

No.  81  (1910). 
CARPENTER,   L.  G.    Seepage  or  Return  Waters  from  Irrigation. 

Colorado  Experiment  Station,  Bulletin  No.  33  (1896). 
CARPENTER,  L.  G.   The  Loss  of  Water  from  Reservoirs  by  Seepage 

and  Evaporation.    Colorado  Experiment  Station,  Bulletin  No. 

45  (1898). 
CARPENTER,  L.  G.    Losses  from  Canals  from  Filtration  or  Seepage. 

Colorado  Experiment  Station,  Bulletin  No.  48  (1898). 
DORSET,  CLARENCE  W.    Alkali  Soils  of  the  United  States  (contains 

United  States  literature).    United  States  Department  of  Agri- 
culture, Bureau  of  Soils,  Bulletin  No.  35  (1906). 
DORSEY,  CLARENCE  W.    Reclamation  of  Alkali  Land  in  Salt  Lake 

Valley,    Utah.     United    States    Department    of    Agriculture, 

Bureau  of  Soils,  BuUetin  No.  43  (1907). 
DORSEY,  CLARENCE  W.    Reclamation  of  Alkali  Soils  at  Billings, 

Montana.    United  States  Department  of  Agriculture,  Bureau 

of  Soils,  Bulletin  No.  44  (1907). 
ELLIOT,  C.  G.    Development  of  Methods  of  Drainage  for  Irrigated 

Lands.    United  States  Department  of  Agriculture,  Office  of 

Experiment  Stations,  Annual  Report  for  1910. 
ELLIOT,  C.  G.    Drainage  of  Farm  Lands.    United  States  Depart- 
ment of  Agriculture,  Farmers'  Bulletin  No.  187  (1904). 
ETCHEVERRY,  B.  A.    Increasing  the  Duty  of  Water.    California 

Experiment  Station,  Circular  No.  114  (1914). 
FLEMING,   B.  P.    Seepage  Investigations.    Wyoming  Experiment 

Station,  Bulletin  No.  61  (1904). 
FITTERER,  J.  E.   Reclamation  by  Drainage.   Wyoming  Experiment 

Station,  BuUetin  No.  90  (1911). 


404  IRRIGATION  PRACTICE 

FULLER,  MYRON  L.  Summary  of  the  Controlling  Factors  of  Artesian 

Flows.     United  States  Geological  Survey,   Bulletin  No.   319 

(1908). 
FULLER,  MYRON  L.    Underground  Waters  for  Farm  Use.    United 

States  Geological  Survey,  Water  Supply  Papers  No.  255  (1910). 
FORTIER,  SAMUEL,  and  CONE,  VICTOR  M.    Drainage  of  Irrigated 

Lands  in  the  San  Joaquin  Valley,  California.    United  States 

Department   of   Agriculture,   Office   of  Experiment   Stations, 

Bulletin  No.  217  (1909). 
HEADDEN,  W.  P.   The  Fixation  of  Nitrogen  in  Some  Colorado  Soils. 

Colorado  Experiment  Station,  Bulletins  Nos.  155,  178  and  186 

(1913). 
HEADDEN,  W.  P.   Deterioration  in  the  Quality  of  Sugar  Beets,  Due 

to  Nitrates  Formed  in  the  Soil.    Colorado  Experiment  Station, 

Bulletin  No.  183  (1912). 
HEADDEN,  W.  P.    Destruction  of  Concrete  by  Alkali.    Colorado 

Experiment  Station,  BuUetin  No.  132  (1908). 
HILGARD,  E.  W.   Soils.   The  Macmillan  Company  (1906). 
KEARNEY,  THOMAS  H.   The  Wilting  Coefficient  for  Plants  in  Alkali 

Soils.    United  States  Department  of  Agriculture,  Bureau  of 

Plant  Industry,  Circular  No.  109  (1913). 
KEARNEY,  THOMAS  H.,  and  HARTER,  L.  L.   Comparative  Tolerance 

of  Various  Plants  for  the  Salts  Common  in  Alkali  Soils.   United 

States  Department  of  Agriculture,  Bureau  of  Plant  Industry, 

Bulletin  No.  113  (1907). 
LOUGHRIDGE,  R.  H.   Tolerance  of  Eucalyptus  for  Alkali.   California 

Experiment  Station,  Bulletin  No.  225  (1911). 
MACHIE,  W.  W.    Reclamation  of  White-Ash  Lands  Affected  with 

Alkali  at  Fresno  California.     United  States  Department  of 

Agriculture,  Bureau  of  Soils,  Bulletin  No.  42  (1907). 
MEAD,  ELWOOD.   Report  of  Irrigation  and  Drainage  Investigations, 

1904.     United   States   Department   of  Agriculture,   Office   of 

Experiment  Stations,  Annual  Report  for  1904. 
MEAD,  ELWOOD,  and  ETCHEVERRY,  B.  A.    Lining  qf  Ditches  and 

Reservoirs  to  Prevent  Seepage  Losses.    California  Experiment 

Station,  Bulletin  No.  188  (1907). 
MEANS,  THOMAS  H.  Reclamation  of  Alkali  Lands  in  Egypt.  United 

States  Department  of  Agriculture,  Bureau  of  Soils,  Bulletin 

No.  21  (1903). 


OVER-IRRIGATION  AND  ALKALI  405 

SCHLICHTER,  CHARLES  S.  The  Rate  of  Movement  of  Underground 
Waters.  United  States  Geological  Survey,  Water  Supply 
Papers,  No.  140  (1905). 

SMITH,  G.  E.  P.  Cement  Pipe  for  Small  Irrigating  Systems  and 
Other  Purposes.  Arizona  Experiment  Station,  Bulletin  No.  55 
(1907). 

STEWART,  ROBERT,  and  GREAVES,  J.  E.  The  Movement  of  Nitric 
Nitrogen  in  Soil  and  Nitrogen  Fixation.  Utah  Experiment 
Station,  Bulletin  No.  115  (1911). 

TANNATT,  E.  TAPPAN,  ANDERSON,  A.  P.,  and  KNEALE,  R.  D.  Seepage 
and  Drainage.  Montana  Experiment  Station,  Bulletin  No.  65 
(1907),  and  No.  76  (1909). 

TANNATT,  E.  TAPPAN,  and  BURKE,  EDMUND.  The  Effect  of  Alkali 
on  Portland  Cement.  Montana  Experiment  Station,  Bulletin 
No.  68  (1908). 

TEELE,  R.  P.  Review  of  Ten  Years  of  Irrigation  Investigations. 
United  States  Department  of  Agriculture,  Office  of  Experi- 
ment Stations,  Annual  Report  for  1908  (separate). 

TEELE,  R.  P.  Losses  of  Irrigation  Water  and  Their  Prevention. 
United  States  Department  of  Agriculture,  Office  of  Experi- 
ment Stations,  Annual  Report  for  1907. 

TALMAGE,  J.  E.  The  Great  Salt  Lake,  Present  and  Past  (1900). 

TRUE,  RODNEY  H.,  and  BARTLETT,  HARLEY,  HARRIS.  Absorption 
and  Secretion  of  Salts  by  Roots  as  Influenced  by  Cultural 
Solutions.  United  States  Department  of  Agriculture,  Bureau 
of  Plant  Industry,  Bulletin  No.  231  (1912). 

WTIDTSOE,  J.  A.,  and  STEWART,  ROBERT.  The  Soil  of  the  Southern 
Utah  Experiment  Station.  Utah  Experiment  Station,  Bulletin 
No.  121  (1913). 

WOODWARD,  S.  M.  Land  Drainage  by  Means  of  Pumps.  United 
States  Department  of  Agriculture,  Office  of  Experiment  Sta- 
tions, Bulletin  No.  243  (1911). 

WRIGHT,  J.  O.  Swamp  and  Overflowed  Lands  in  the  United  States. 
United  States  Department  of  Agriculture,  Office  of  Experi- 
ment Stations,  Circular  No.  76  (1907). 


CHAPTER  XIX 
IRRIGATION  IN  HUMID  CLIMATES 

IRRIGATION  should  always  be  practised  to  supplement 
the  natural  rainfall.  Where  there  is  much  rainfall,  either 
during  the  growing  season,  or  in  the  winter,  that  can  be 
stored,  less  irrigation  is  needed  than  where  the  rainfall  is 
low.  Wherever  the  rainfall  is  not  high  enough  to  yield 
maximum  crops,  however,  irrigation  is  desirable;  and 
wherever  the  rainfall  does  not  come  regularly  during  the 
season  or  from  season  to  season,  irrigation  ensures  steady 
yields.  Only  over  a  small  part  of  the  earth's  surface  is  the 
rainfall  large  enough  or  regular  enough  to  insure  the  high- 
est or  steady  yields.  The  so-called  humid  regions  are 
often  subject  to  droughts,  and  the  soils  of  such  sections  are 
usually  unresistant  to  drought.  The  great  centers  of 
population,  with  their  splendid  markets,  usually  located 
in  humid  sections,  make  it  especially  desirable  that  large 
and  steady  yields  be  obtained  by  the  neighboring  farmers, 
particularly  the  truck-gardeners.  For  these  reasons, 
irrigation  promises  to  become  a  large  practice  under  humid 
conditions. 

Irrigation  in  humid  climates  is  not  new.  Much  of  the 
European  irrigation  is  done  under  a  relatively  high  rain- 
fall. Water  meadows  have  been  known  for  centuries  in 
England,  and  many  have  existed  for  a  half-century  or 
more  in  New  England.  The  practice  of  irrigation  under 
humid  conditions  has  only  recently,  however,  been  con- 
sidered seriously  and  extensively. 

(406) 


IRRIGATION  IN    HUMID  CLIMATES 


407 


242.  Dry  seasons. — It  is  an  elementary  fact  of  weather 
science  that  neither  the  total  annual  rainfall  nor  its  dis- 
tribution is  exactly  the  same  from  year  to  year.  The 
average  of  many  years  does  not,  perhaps,  vary  greatly, 
but  from  year  to  year  there  is  a  considerable  difference. 
This  constitutes  the  main  reason  for  irrigation  in  humid 
districts.  For  instance,  Williams  has  compiled  the  follow- 
ing table  from  the  United  States  Weather  Bureau,  covering 
ten  years,  from  1899  to  1909,  showing  the  average  annual 
rainfall,  the  number  of  droughts  or  periods  of  fifteen  days 
with  less  than  1  inch  of  rainfall,  for  five  points  in  the 
United  States,  representing  five  great  divisions  of  the 
country.  In  the  first  column  is  shown  the  point  at  which 
the  observation  was  made;  in  the  second  column,  the 
average  annual  rainfall  in  inches;  in  the  third  column,  the 
number  of  fifteen-day  periods  or  over  with  less  than  1  inch 
of  ram,  or  periods  of  drought;  in  the  fourth  column,  the 
number  of  days  when  irrigation  was  required,  meaning 
the  number  of  days  beyond  the  fifteen  days  during  which 
less  than  1  inch  rainfall  was  received. 


Stations 

Average 
annual 
rainfall 

Number  of  15-day 
periods  or  over 
with  less  than 
1  inch  of  rain 

Number  of  days 
when  irrigation 
was  required 

Ames,  Iowa      .... 
Oshkosh,  Wis.      .    .    . 
Vineland,  N.  J.    .    .    . 
Columbia,  S.  C.  .    .    . 
Selma,  Ala  

30.39 
29.78 
47.47 
47.55 
50.75 

23 

27 
46 
62 
60 

190 
292 
352 
568 
724 

It  may  be  noted  hi  the  above  table  that  at  Ames, 
Iowa,  with  an  average  rainfall  of  over  30  inches,  there  were, 
in  ten  years,  twenty-three  periods  of  drought,  with  190 
days  when  irrigation  would  have  been  beneficial.  At 


408 


IRRIGATION  PRACTICE 


Oshkosh,  Wisconsin,  with  a  rainfall  of  practically  30 
inches  per  year,  there  were  twenty-seven  such  periods  of 
drought,  sixteen  of  which  came  in  the  spring  and  early 
summer,  and  one  of  which  lasted  fifty-nine  days.  At 
Vineland,  New  Jersey,  with  a  rainfall  of  47  inches,  there 
were  forty-six  such  droughts,  and  362  days  during  which 
irrigation  would  have  been  helpful.  At  Columbia,  South 


FIG.  118.  The  annual  rainfall  of  Milan  (famous  for  its  irrigation),  compared  with 
that  of  humid  and  arid  districts  in  the  United  States. 

Carolina,  of  the  sixty-two  droughts  occurring  in  the  ten 
years,  twenty-seven  lasted  from  twenty  to  thirty  days, 
four  from  forty  to  fifty  days,  and  one  lasted  sixty-one 
days,  showing  the  frequent  occurrence  of  rather  long 
droughts  in  that  section  of  the  country.  At  Selma,  Ala- 
bama, with  over  50  niches  of  rainfall,  sixty  periods  of 
drought  occurred,  with  724  days  needing  irrigation. 

The  facts  of  this  table  are  only  representative  of  a  vast 
mass  of  information  of  a  similar  character  gathered  by  the 


IRRIGATION  IN  HUMID  CLIMATES 


409 


Irrigated 


Not  Irrigated 


'///////////A 


Irrigated 


Weather  Bureau.  No  part  of  the  country,  no  matter 
what  its  total  annual  rainfall  may  be,  is  wholly  free  from 
periods  of  drought.  Occasionally,  these  periods  are  so  long 
and  so  severe  as  to  cause  almost  the  absolute  failure  of 
crops  with  all  the  evils  attending  crop  failure.  It  is  to 
protect  the  farmer  against  such  periods  of  drought  that 
irrigation  in  humid  regions  is  advisable. 

243.  Results  of  irrigation  in  humid  regions. — Irrigation 
in  humid  regions,  as  already  suggested,  is  not  a  new  prac- 
tice; it  has  simply 
failed  to  arouse  any 
large  interest  among  Plat  1 
the  people  living  under 
humid  conditions.  In  2 

recent  years,  consider- 
able  experimental  3 
work   has   been   con- 
ducted   in    various            4 
parts   of   the    humid 
regions  of  the  United 
States,  having  in  view 
the  determination  of 
the  advantage  resulting  from  the  use  of  irrigation  water 
in  localities  that  may  safely  be  classed  as  humid. 

Bowie  investigated  about  125  irrigated  meadows,  in 
four  counties,  in  the  state  of  Pennsylvania,  the  average 
yields  of  which  were  contrasted  with  similar  unirrigated 
meadows  in  the  same  localities.  The  average  of  the  125 
observations  showed  that  irrigation  just  doubled  the  yield. 
In  other  states,  similar  investigations  of  meadows  have 
been  made,  with  practically  the  same  results.  In  the 
eastern  United  States,  irrigation  doubles  the  harvests 
from  ordinary  meadows. 


Not  Irrigated 


'//////////A 


FIG.  119.    Comparative  yields  of  strawberries, 
irrigated    and    unirrigated.        (Connecticut, 

1895J 


410  IRRIGATION  PRACTICE 

Waters  conducted  experiments  under  Missouri  con- 
ditions, and,  while  the  work  was  not  continued  long 
enough  to  give  averages  for  a  variety  of  climatic  con- 
ditions, it  was  found  that  a  great  increase  in  the  yield 
resulted  from  the  application  of  irrigation  water.  As- 
paragus, grown  without  irrigation,  was  thin  and  covered 
with  rust;  when  irrigated  it  was  plump  and  free  from  rust. 
Yield  and  quality  were  increased  by  irrigation.  Onions 
and  corn  both  yielded  larger  crops  under  irrigation. 

Crane,  working  under  South  Dakota  conditions,  found 
that  every  crop  he  investigated  yielded  twice  as  much 
when  irrigation  water  was  applied.  His  studies  were 
almost  entirely  with  artesian  water,  and  the  increase  in 
crop-yields  proved  abundantly  that  whenever  such  waters 
can  be  obtained  they  may  be  used  with  great  profit. 

Voorhees  carried  on  extensive  investigations,  chiefly 
during  the  years  1898  and  1899,  to  discover  if  the  use  of 
irrigation  water  influenced  materially  the  yield  of  crops  in 
New  Jersey.  He  found,  as  expected,  that  the  season  is  the 
important  factor  in  determining  the  value  of  irrigation. 
If  the  growing  season  was  an  abundantly  wet  one,  irrigation 
had  less  effect  than  when  the  season  was  relatively  dry. 
The  averages  of  the  results  obtained  by  Voorhees  for  the 
two  years  in  question  are  exceedingly  instructive. 

Blackberries,  several  varieties  of  which  were  tried, 
showed  an  increase,  due  to  irrigation,  of  nearly  77  per 
cent  of  the  yield  without  irrigation.  Raspberries,  repre- 
sented by  several  varieties,  increased  over  37  per  cent, 
varying  from  70  per  cent  to  a  loss  when  the  natural  pre- 
cipitation was  high.  Currants,  represented  by  a  number 
of  varieties,  increased  over  28  per  cent,  varying  from  91 
to  a  loss.  Gooseberries,  represented  by  a  number  of  va- 
rieties, increased  3.3  per  cent,  varying  from  109  per  cent 


IRRIGATION  IN  HUMID  CLIMATES  411 

to  a  loss.  That  is,  every  experiment  undertaken  by 
Voorhees  yielded  average  large  returns,  for  small  fruits, 
by  the  application  of  irrigation  water.  Phelps,  working 
in  Connecticut,  in  1895,  obtained  similar  results.  Straw- 
berries grown  under  irrigation  in  Connecticut  yielded  a 
harvest  159  per  cent  greater  than  that  obtained  without 
irrigation. 

King  conducted  a  long  series  of  similar  experiments 
under  Wisconsin  conditions,  and  his  results  confirm,  in 
every  particular,  the  conclusions  of  other  investigators. 
King  found  that  irrigation  increased  the  yield  of  potatoes 
46  per  cent;  cabbage,  12  per  cent;  corn,  55  per  cent;  and 
clover,  barley,  strawberries,  and  many  other  crops  under 
experimentation  showed  large  increases  under  irrigation. 
Maxwell  studied,  for  a  number  of  years,  sugar-cane  irri- 
gation in  the  Hawaiian  Islands,  under  an  annual  pre- 
cipitation of  about  47  inches.  During  the  year  1897-98  the 
yield  of  sugar  was  increased  nearly  1,500  per  cent  by  irri- 
gation. 

It  may  be  that  these  large  increases  from  irrigation 
are  partly  due  to  the  fact  that  under  irrigation  much 
closer  planting  is  allowed  without  drying  out  the  soil. 
However  that  may  be,  the  increase  is  really  due  to  the 
fact  that  there  is  no  shortage  of  water  during  the  growing 
period.  It  has  been  amply  demonstrated  that  the  arti- 
ficial application  of  water  on  humid  lands  does  increase 
the  harvests.  Whether  the  increase  and  certainty  of 
crop-yield  will  pay  for  the  cost  of  building  the  irrigation 
system  and  of  applying  the  water  must  be  worked  out  by 
each  farmer  in  accordance  with  the  conditions  that  sur- 
round him.  Field  crops  which  yield  a  small  acre  return 
may  not  pay  for  irrigation,  but  truck  crops,  yielding  large 
acre  returns,  will  often  pay  in  one  season  for  the  instal- 


412 


IRRIGATION  PRACTICE 


lation  of  the  irrigation  plant  and  leave  a  margin  besides. 
Irrigation  in  humid  climates  probably  always  pays,  unless 
exceptional  difficulties  are  encountered  in  securing  and 
distributing  water.  One  drought,  unprovided  against, 
frequently  causes  a  loss  that  would  pay  for  the  irrigation 
system  and  much  else. 

244.  Methods  of  applying  water. — The  methods  of 
applying  water  in  humid  regions  are  those  in  general  use 


Reservoir 


Public  Road 


FIG.  120.  An  irrigation  plant  in  Pennsylvania 


everywhere.  Furrowing  is  probably  best,  except  where 
the  soil  is  very  clayey,  or  where  meadows  are  flooded  with 
water.  In  humid  regions,  on  many  relatively  small  tracts 
devoted  to  irrigation,  specialized  crops  are  usually  grown, 
yielding  high  acre  returns.  Under  such  conditions  it  is 
often  feasible  to  install  special  irrigation  devices,  such  as 
sprinkling  from  permanently  fixed  pipes  or  from  the  nozzles 
of  movable  hose.  Such  methods  are  wasteful  of  invest- 
ment, labor  and  water  and  are  practically  out  of  the  ques- 
tion for  large  areas.  Sub-irrigation  also  is  advocated  under 
humid  conditions,  but  the  arguments  already  urged  against 
sub-irrigation,  unless  natural,  hold  under  humid  condi- 


IRRIGATION  IN  HUMID  CLIMATES  413 

tions.  There  should  be  no  differentiation  in  the  irrigation 
practices  of  humid  and  arid  regions.  In  both  regions  there 
should  be  an  adaptation  of  the  general  principles  to  the 
special  needs  of  the  community. 

245.  The  duty  of  water. — Since  irrigation  is  merely 
supplementary  to  the  rainfall,  less  irrigation  water  is  ordi- 
narily required  in  humid  regions  than  in  arid  regions. 
One  to  3  inches  of  water  applied  at  each  irrigation  is 
common    under    humid    conditions,    and    is    apparently 
abundant.    In  arid  regions,  on  the  other  hand,  3  to  5 
inches,  or  even  more,  are  applied  at  each  irrigation.    In 
the  humid  regions,   plants  are  likely  to  be  somewhat 
shallow-rooted,  owing  to  the  abundance  of  moisture  in  the 
early  growing  season.    This  makes  it  unnecessary  for  the 
roots  to  move  deeply  in  the  soil  and  therefore  more 
frequent  irrigation  is  probably  necessary  than  in  arid 
regions.    However,  the  application  of  water  every  ten  or 
fifteen  days  should  be  sufficient.    In  general,  the  duty  of 
water  in  humid  regions  should  be  higher  than  in  arid 
regions,  but  this  does  not  always  follow,  for  it  is  reported 
that  to  irrigate  sugar  cane,  under  humid  conditions,  a 
depth  of  water  equivalent  to  40  to   100  inches  is  used 
throughout  the  season,  which  is  much  more  than  is  neces- 
sary in  the  arid  regions.    It  is  probable  that,  in  humid  as 
in  arid  regions,  the  tendency  will  be  to  use  too  much 
water.    Over-irrigation  is  just  as  objectionable  in  humid 
as  in  arid  climates,  and  for  the  reasons  already  stated 
in  previous  chapters. 

246.  Sources  of  water. — The  humid  region  abounds 
in  creeks,  ponds,  rivers  and  underground  water,  all  of 
which  are  suitable  for  irrigation.    However,  water-rights 
in  the  East,  where  irrigation  has  received  little  attention, 
are  more  complicated,  and  frequently  it  is  more  difficult 


414  IRRIGATION  PRACTICE 

there  than  in  the  West  to  claim  water  for  agricultural 
purposes.  Consequently  irrigation  in  the  humid  regions, 
at  least  in  the  beginning,  must  be  more  of  individual 
effort  and  less  of  community  action.  Independent,  small 
plants  must  be  established,  which,  in  time,  may  lead  to 
cooperation.  Meanwhile,  many  natural  waters  may  be 
impounded;  springs  may  be  enlarged,  water  may  be  lifted 
by  the  stream  current  from  the  rivers,  windmills  and  other 
engines  may  be  made  to  lift  water  from  wells,  and  artesian 
waters  may  be  developed.  Since  underground  water  is 
more  available  under  humid  conditions  than  under  arid 
conditions,  the  pumping  plant  may  become  a  chief  de- 
pendence on  the  irrigated  farms  of  the  East.  Such  pump- 
ing plants  need  be  in  operation  only  at  the  very  time  that 
water  is  needed  for  the  farms. 

247.  Water-conservation    methods. — In    the    humid 
regions,  the  farmer  has  depended  on  the  rainfall  and  has 
given  little  attention  to  cultural  methods  for  conserving 
water.     Beyond  question,   humid  agriculture  would  be 
greatly  improved  if  the  farmers  should  adopt  the  simple 
methods  of  dry-farming  for  storing  and  retaining  the 
water  that  falls  upon  the  soil,  by  proper  plowing,  surface 
tillage  and  other  methods.    This,  alone,  would  eliminate 
many  of  the  droughts  that  trouble  the  humid  regions. 
Irrigation,  then,  would  need  to  be  called  less  frequently 
into  service.     Before  the   droughts   of  the  world  shall 
finally  cease  to  vex  man,  it  is  necessary  for  both  dry- 
farming  and  irrigation  methods  to  be  adopted  in  the 
humid  regions  of  the  world. 

248.  Value  of  sewage  water. — Sewage  irrigation,  while 
not  necessarily  practised  under  a  high  rainfall,  is  closely 
associated  with  irrigation  in  humid  regions  for  the  reason 
that  most  of  the  larger  cities,  boasting  the  largest  quan- 


IRRIGATION  IN  HUMID  CLIMATES  415 

tity  of  sewage,  are,  as  yet,  located  under  a  considerable 
rainfall.  The  materials  dissolved  or  suspended  in  irrigation 
water  are  often,  as  shown  in  Chapter  V,  of  high  value  as 
plant-food.  Of  all  known  waters,  however,  sewage  water 
is  usually  of  the  highest  value  hi  crop-growth,  since  its 
chief  constituent,  human  waste,  approaches  in  composition 
the  more  valuable  portions  of  plants. 

It  has  been  roughly  calculated  that  each  person,  living 
in  a  city,  wastes  annually  eight  pounds  of  nitrogen,  three 
pounds  of  potassium,  two  pounds  of  phosphorus,  not 
counting  the  organic  matter  of  which  these  three  funda- 
mentally important  elements  are  parts.  When  these 
quantities  are  multiplied  by  the  millions  residing  in  many 
of  the  large  cities,  the  sewage  which  passes  into  the  rivers 
and  oceans,  rises  to  tremendous  value.  The  large  cities 
cause  the  largest  single  losses,  but  the  smaller  cities  of  the 
country  are  now  installing  sewage  systems,  and  all  should 
give  some  attention  to  the  conservation  of  sewage  waste. 
Sewage  can  best  be  put  to  use  by  its  application  in  irri- 
gation. 

249.  The  use  of  sewage. — In  many  countries,  sewage 
water  is  used  for  plant-production.  The  most  famous 
example  is  that  of  Craigentinny  meadows,  receiving  sewage 
from  Edinburgh.  According  to  Storer  and  King,  one 
hundred  years  ago,  when  sewage  irrigation  began  on  these 
fields,  they  were  originally  a  waste.  With  the  aid  of  sewage 
irrigation  they  have  produced  continuously  since  that  time 
large  crops  of  grass,  with  a  profit  far  above  that  of  the 
best  fields  of  the  country.  Similarly,  near  Milan  hi  Italy, 
sewage  is  let  into  great  canals  that  lead  to  great  meadows. 
These  have  produced  remarkably,  as  a  result  of  the  appli- 
cation of  the  heavily  fertilized  water.  China,  and  the 
Orient  generally,  are  perhaps  the  greatest  examples  of  the 


416 


IRRIGATION  PRACTICE 


wise  use  of  human  waste  in  crop-production.  In  these 
countries,  modern  sewage  systems  have  not  been  installed, 
but  the  human  waste  is  carried  in  specially  provided  re- 
ceptacles to  the  farms.  It  is  not  likely  that  this  method 
will  be  adopted  under  civilized  conditions;  human  waste 
will  continue  to  be  thrown  into  sewage  systems,  but,  as 
among  the  Chinese  and  other  nations  that  have  estab- 
lished a  permanent  system  of  agriculture,  the  sewage 


FIG.  121.  Distribution  of  water  on  Craigentinny  Meadows,  Edinburgh. 

water  thus  produced  must  be  used  for  the  production  of 
crops. 

It  has  been  argued  that,  for  health  reasons,  sewage 
should  not  be  so  used,  for  disease  germs  might  be  carried 
by  sewage  water  to  the  herbage  and  thence  to  domestic 
animals  and  finally  to  human  beings.  The  fact  that  sewage 
irrigation  has  been  practised  for  centuries  with  no  evi- 
dence of  such  evil  effects  leads  to  the  belief  that  the 
danger  does  not  exist.  Sewage,  if  properly  applied  to  a 
soil  which  is  properly  tilled,  is  thoroughly  oxidized  and 
becomes  innocuous.  Plants,  themselves,  would  not  be 


IRRIGATION  IN  HUMID  CLIMATES  417 

likely  to  take  up  disease  germs.  Every  open  water  channel, 
especially  in  settled  sections,  contains  to  some  degree  the 
substances  of  ordinary  sewage,  yet  none  hesitate  to 
use  such  water  for  irrigation  purposes.  The  matter  could 
well  be  subjected  to  experimental  inquiry,  before  extensive 
sewage  irrigation  is  undertaken. 

It  is  ordinarily  quite  difficult  to  make  the  best  use  of 
sewage  water,  because  the  outlets  of  sewage  systems  are 
usually  in  low  places,  and  the  main  problem  is  that  of 
lifting  water  to  fields.  However,  in  many  places  it  is  pos- 
sible to  take  out  the  river  water  some  distance  below  the 
outlet  of  the  system  and  there  to  apply  it  to  fields.  In 
other  places,  the  sewage  might  be  run  into  reservoirs  and 
then  be  pumped  to  the  fields. 

250.  Factory  and  mill  waste. — While,  in  general,  sew- 
age waters  are  admirably  adapted  to  the  production  of 
vegetable  matter,  yet  it  must  not  be  forgotten  that 
certain  kinds  of  waste  are  detrimental  to  plant  growth. 
For  instance,  the  sewage  or  waste  from  certain  factories 
and  mills  is  injurious.  In  the  West,  it  has  been  found  fre- 
quently that  waters  coming  from  gold  and  silver  mills 
contain  poisonous  elements.  Copper  mills  have  likewise 
been  shown  to  contaminate  water  to  such  a  degree  that 
its  irrigation  value  is  greatly  reduced.  Attention  should 
be  given,  even  in  the  open  country,  to  the  possible  con- 
tamination of  water  by  substances  which  are  injurious  to 
plants  and  animals. 

REFERENCES 

BOWIE,  AUG.  J.,  Jr.  Irrigation  in  the  North  Atlantic  States.  United 
States  Department  of  Agriculture,  Office  of  Experiment  Sta- 
tions, Bulletin  No.  167  (1906) 

KING,  F.  H.    Irrigation  in  Humid  Climates.   United  States  Depart- 
ment of  Agriculture,  Farmers'  Bulletin  No.  46  (1896). 
AA 


418  IRRIGATION  PRACTICE 

KING,  F.  H.  Farmers  of  Forty  Centuries.  Mrs.  F.  H.  King,  Madison, 
Wisconsin  (1911). 

MAXWELL,  WALTER.  Irrigation  in  Hawaii.  United  States  Depart- 
ment of  Agriculture,  Office  of  Experiment  Stations,  Bulletin 
No.  90  (1900). 

MEAD,  ELWOOD.  Irrigation  Investigations  in  Humid  Sections  of 
the  United  States  in  1903.  United  States  Department  of  Agri- 
culture, Office  of  Experiment  Stations,  Bulletin  No.  148  (1904). 

PHELPS,  C.  S.,  and  VOORHEES,  EDWARD  B.  Notes  on  Irrigation  in 
Connecticut  and  New  Jersey.  United  States  Department  of 
Agriculture,  Office  of  Experiment  Stations,  Bulletin  No.  36 
(1897). 

VOORHEES,  EDWARD  B.  Irrigation  in  New  Jersey.  United  States 
Department  of  Agriculture,  Office  of  Experiment  Stations, 
Bulletin  No.  87  (1900). 

WILLIAMS,  MILO  B.  Possibilities  and  Needs  of  Supplemental  Irri- 
gation in  the  Humid  Regions.  United  States  Department  of 
Agriculture,  Yearbook  for  1911. 

YODER,  P.  A.  Poison  in  Water  from  a  Gold  and  Silver  Mill.  Utah 
Experiment  Station,  Bulletin  No.  81  (1903). 


CHAPTER  XX 
IRRIGATION  TOOLS  AND  DEVICES 

FARMING  under  irrigation  may  and  does  use  practically 
every  approved  farm  tool  found  desirable  under  humid 
conditions.  Every  refinement  known  to  agriculture  may 
be  practised  with  profit  by  the  farmer  under  the  ditch. 
Plowing  at  the  correct  time,  to  the  best  depth  and  by  the 
accepted  methods,  lies  at  the  foundation  of  successful 
irrigation-farming  and  humid-farming.  To  plant  correctly; 
to  supply  the  plants  with  sufficient  food;  to  remove  weeds, 
and  to  harvest  wisely — are  all  practices  to  be  observed  as 
carefully  by  the  irrigation-farmer  as  by  the  rainfall- 
farmer. 

The  special  tools  and  devices  for  irrigation  farming  are 
those  only  that  are  used  directly  for  the  distribution  upon 
the  land  of  water  from  the  canal  and  the  conservation  of 
it  in  the  soil. 

251.  Clearing  and  breaking  the  land. — The  pioneer 
irrigationist  will  usually  find  his  new  farm  unbroken. 
It  is  either  covered  by  sage-brush  or  similar  plants  or  in 
the  firm  sod  of  the  plains.  Sod  land  may  be  easily  broken 
by  a  breaking  plow,  many  forms  of  which  are  found  on  the 
market. 

Sage-brush  land  is,  however,  much  more  difficult  to 
clear.  One  of  the  most  effective  methods  is  to  drag  over 
the  land  two  parallel  railroad  irons  which  pull  up  most  of 
the  sage-brush.  The  remaining  clumps  must  be  grubbed 
out  by  hand.  Sometimes  the  railroad  irons  are  joined  in  a 

(419) 


420 


IRRIGATION  PRACTICE 


V-shape,  and  shod  on  the  outside  with  iron  cutting-edges. 
Such  an  iron  "snow-plow"  is  also  very  effective  in  clearing 
sage-brush  from  the  land.  The  most  effective  method, 
when  it  can  be  used,  is  to  burn  off  the  brush.  In  the  inter- 
mountain  country  with  dry  summers,  the  brush  often 
becomes  very  dry  in  late  summer,  and  on  a  day  when  a 
light  wind  is  blowing  it  may  be  possible  to  remove  the 
brush  from  a  large  area.  The  obvious  dangers  that 
accompany  fire  must  always  be  considered.  Many 
machines  are  on  the  market  for  removing  sage-brush; 


FIG.    123.    Section    of 
V-shaped  flume. 


FIG.  124.  Wooden  flume.  FIG.  125.  Section  of  rectangular  flume. 

none  are  wholly  satisfactory,  and  as  the  country  is  taken 
up,  there  will  be  no  further  need  for  them. 

252.  Laying  out  the  farm. — Once  the  land  has  been 
cleared,  the  farm  should  be  laid  out  with  reference  to  the 
crops  to  be  grown,  rotations  to  be  followed,  and  the  most 
effective  methods  of  applying  water.  The  characteristic 
feature  of  farming  under  irrigation  makes  it  of  first 
importance  that  the  lay-out  be  made  with  direct  reference 
to  the  location  of  the  irrigation  ditches  that  must  cover 


IRRIGATION  TOOLS  AND  DEVICES 


421 


the  farm.  This  should  be  done  with  extreme  care,  for 
any  mistakes  made  in  the  placing  of  irrigation  ditches  will 
mean  loss  in  tune  and  money  when  a  new  system  is  built. 

In  general,  water 
should  be  delivered 
from  the  supply  lateral 
at  the  highest  point 
of  the  farm.  This 
makes  it  possible  to 
distribute  water  over 
the  whole  farm.  In 
earlier  days,  all  the 
farm  ditches  were 
carried  along  ridges 
or  high  lines  of  the 
farm.  This  method 
led  to  the  formation  of  irregular  and  somewhat  unsightly 
fields,  awkward  to  fit  into  a  system  of  rotation.  While  it 
is  indispensable  that  the  farm  ditches  follow,  in  a  general 
way,  the  contour  lines  of  the  farm,  yet  an  irrigated  farm 
may  be  laid  off  into  regular,  rectangular  fields  by  the 
use  of  special  devices  to  carry  the  water  across  depres- 
sions of  the  land. 

The  most  common  method  of  securing  straight  ditches 
on  the  farm  is  the  use  of  earthen  levees,  to  carry  the 


FIG.  126.  Flume  with  lateral  gate. 


FIG.  127.  Buck  scraper. 


422 


IRRIGATION  PRACTICE 


FIG.  128.  Leveler  or  float. 


water  across  the  low  places.  Earthen  levees  cost  little 
and  may  be  made  by  the  farmer,  and,  although  subject 
to  frequent  washouts  during  the  first  two  or  three  years, 
give  no  further  trouble  after  they  are  once  established.  A 
more  desirable  method,  when  it  can  be  afforded,  is  the 
flume  or  the  pipe  to  carry  water  across  low  places.  Tri- 
angular and  rectangular  flumes  are  used.  Wooden  flumes 


Fio.  129.  Shuart  grader. 


IRRIGATION  TOOLS  AND  DEVICES 


423 


give  very  good  satisfaction  while  they  last,  but  are  not 
so  permanent  as  the  concrete  flumes  which  are  now  being 
constructed  extensively.  Recently,  also,  galvanized  iron 
pipes  or  concrete  pipes  are  used  with  success  for  carrying 
water  over  the  farm. 

The  second  guiding  principle  in  laying  out  the  ditches 
on  the  farm  should  be  that  they  be  as  inconspicuous  as 
possible  and  out  of  the  way  of  the  regular  operations  on 
the  farm.  For  that  reason  the  _ 
ditches  are  often  made  to  follow 
the  fences  separating  the  farm  fields, 
and  are  even  buried  underground  as 
pipes,  with  openings  at  proper  places 
to  supply  the  smaller  laterals.  (Figs. 
122-125.) 

253.  Leveling  the  land. — Natural 
land  is  seldom  of  even  or  regular  sur- 


FIG.  130.  Soil  auger. 


Fio.  131.  Lateral  plow. 


424 


IRRIGATION  PRACTICE 


FIG.  132.    V-crowder. 

face.  Slight  elevations  and  depressions  cover  it.  The 
more  even  the  land  is,  however,  the  more  easily  and 
uniformly  may  irrigation  water  be  applied.  Water 
applied  to  uneven  land  accumulates  in  the  lower  places 
and  over-irrigates  the  plants  there  growing,  while  the 
plants  on  the  higher  places  receive  little  or  no  water. 
Consequently,  the  yield  of  the  crop  is  reduced.  Moreover, 

such  irrigation  re- 
quires much  labor, 
and  is  unsightly.  As 
soon  as  the  layout 
of  the  farm  has  been 
decided  upon,  steps 
should  be  taken  to 
grade  or  level  the 
land.  The  work  once 

done    properly    need 

FIG.  133.  Building  a  ditch.  not  be    done   again, 


TVPlCflL    FORMS 

FORM     PITCHEIS 


•  -^xggsrz&gr 

Another  form   of    INO.-4. 


FIG.  134.  Typical  torms  of  farm  ditches. 


426 


IRRIGATION  PRACTICE 


and  from  the  first  irrigation  may  be  done  in  the  best 
manner. 

Land  may  be  leveled  by  any  of  the  many  machines  on 
the  market.    The  regular  scrapers  or  graders  may  be  used 


FIG.  135.  Concrete  drop  in  ditch. 

for  reducing  the  high  points,  and  plank-levelers  or  floats 
may  be  used  for  the  final  grading.  (Figs.  127-129.)  In 
cutting  down  the  high  places,  it  is  well  to  know  something 
of  the  subsoil.  If  the  top  soil  is  underlaid  near  the  surface 
with  a  lifeless  clay  it  may  not  be  wise  to  carry  the  grading 
too  low,  or  especially,  to  scatter  the  clay  on  the  lower- 
lying  land.  In  such  cases,  slight  grading  through  successive 
years  may  be  more  satisfactory.  For  studying  the  sub- 
soil, a  soil  auger  is  very  useful.  (Fig.  130.) 

254.  Making  farm  ditches. — After  the  layout  of  the 
farm  has  been  decided  upon,  the  main  supply  ditches 
placed,  and  the  land  leveled,  the  farmer  may  construct 
the  necessary  laterals  or  farm  ditches,  fed  by  the  larger 
supply  ditches.  The  location  of  the  farm  ditches  must  be 


IRRIGATION  TOOLS  AND  DEVICES 


427 


determined  by  the  layout  and  contour  of  the  farm.  All 
ditches,  whether  large  or  small,  must  follow,  in  general, 
the  ridges  of  the  land. 

Farm  ditches  may  be  made  by  any  machine  that  will 
make  a  furrow  in  the  ground.  The  first  modern  irrigation 
ditch  in  America  was  made  by  an  ordinary  moldboard 
plow,  the  furrow  from  which  was  cleaned  out  with  shovels. 
Thousands  of  small  farm  ditches  have  been  made  in  that 
way  since  that  first  day  of  irrigation.  The  lateral  plow  or 
winged  shovel  plow  is  now  more  frequently  used  in  ditch- 


FIG.  136.  Drop  in  flume. 


428 


IRRIGATION  PRACTICE 


making.    (Fig.  131.)    The  adjustable  crowder,  as  shown  in 
Fig.  132,  is  extensively  used  in  removing  the  loose  dirt 


LAR6EL  COLLAR 


FIG.  137.  Distributor  for  hose. 

from  the  plow  furrow.    If  the  ditch  is  large,  the  scraper  is 
used  for  that  purpose. 

Farm  ditches  must  be  constructed  with  reference  to 
the  quantity  of  water 
required  by  the  land 
that  they  are  to  serve. 
The  quantity  of  water 
that  may  be  carried 
by  a  ditch  depends 
fully  as  much  upon 
its  fall  or  grade  as 
upon  its  width  and  depth.  The  smaller  the  volume 
B  carried  by  a  ditch,  the  greater  the  grade 
required  to  secure  the  same  velocity 
of  flow.  In  a  small  ditch  capable 
of  carrying  about  \y%  second- 
feet  of  water,  a  fall  of  2 
inches  to  the  rod 


FIG.  138.  Attaching  hose  to  distributor. 


FIG.  139.  Leveling  device. 


IRRIGATION  TOOLS  AND  DEVICES 


429 


would  produce  a  velocity  of 
2  feet  a  second,  while  in  a 
ditch  capable  of  carrying  about 
24  second-feet,  the  fall  re- 
quired to  give  the  same  veloc- 
ity would  be  only  M  mch  to 
the  rod.  The  nature  of  the 
soil  determines  chiefly  the 
grade  that  may  be  adopted 
for  farm  ditches.  In  fine  sand 
or  silt  a  mean  velocity  of  1 


FIG.  142.  Dammer. 


FIQ.  143.  Board 

da.  in. 


FIG.  147.    Distribution  of  water  from  flume 
to  furrows. 


- 


FIG.  145.  Canvas  dam  with  opening. 


FIG.  148.  Distribution  through  wooden  tubes. 

(430) 


IRRIGATION  TOOLS  AND  DEVICES 


431 


foot  per  second  is  often  the  maximum,  while  in  clay,  a 
velocity  of  3  feet  per  second  may  be  adopted.  Some  soils 
"wash"  so  easily  that  a  very  small  velocity  only  may  be 
used.  The  farmer 
must  learn  for  himself 
the  nature  of  his  soil 
and  the  ditch  grades 
that  may  be  safely 
adopted.  In  ordinary 
materials  a  velocity 
of  2  to  2J/2  feet  a 
second  are  considered 
safe.  Naturally  the 
grade  of  the  ditch  can  not  exceed  that  of  the  land. 
Fortier  has  figured  the  flow  of  water  in  each  of  five 
types  of  farm  ditches  (Fig.  134)  which  cover  ordinary 
farm  conditions.  His  results  follow. 


FIG.  149.  Lath  check. 


tto'fots'  »it  ^o'/9 **ljL_ idto £J'-4 


FIG.  150.  Conducting  water  down  inclines  in  concrete  pipes. 


432 


IRRIGATION  PRACTICE 


MEAN  VELOCITY  AND  DISCHARGE  OF  DITCHES  WITH  DIFFERENT 

GRADES 
Farm  Ditch  No.  1 


Grade 

Mean  velocity 
in  feet  per 
second 

Discharge  in 
cubic  feet 
per  second 

Inches 
per  rod 

Feet  per 
100  feet 

Feet  per 
mile 

Y2 

.25 

13.33 

1.01 

.67 

M 

.38 

20.00 

1.23 

.81 

1 

.51 

26.67 

1.42 

.93 

1M 

.63 

33.33 

1.59 

1.05 

iy2 

.76 

40.00 

1.75 

1.16 

2 

1.01 

53.33 

2.04 

1.35 

2^ 

1.26 

66.67 

2.28 

1.50 

3 

1.51 

80.00 

2.50 

1.64 

3M 

1.77 

93.33 

2.70 

1.78 

FIG,  151.  Roller  furrower, 


IRRIGATION  TOOLS  AND  DEVICES 


433 


MEAN  VELOCITY  AND  DISCHARGE  OF  DITCHES  WITH  DIFFERENT 
GRADES,  Continued 

Farm  Ditch  No.  2 


Grade 

Mean  velocity 

Discharge  in 

Inches 
per  rod 

Foot  per 
100  feet 

Feet  per 
mile 

in  feet  per 
second 

cubic  feet 
per  second 

X 

.13 

6.67 

.82 

80 

l/2 

.25 

13.33 

1.16 

.00 

X 

.38 

20.00 

1.42 

.30 

1 

.51 

26.67 

1.64 

.50 

1M 

.63 

33.33 

1.84 

.70 

IX 

.76 

40.00 

2.02 

.80 

IX 

.88 

46.67 

2.18 

2.00 

2 

1.01 

53.33 

2.34 

2.10 

2y2 

1.26 

66.67 

2.61 

2.40 

Farm  Ditch  No  4 


Farm  Ditch  No.  3 

X 

.06 

3.33 

.79 

2.08 

% 

.13 

6.67 

1.13 

3.00 

X 

.25 

13.33 

1.60 

4.20 

X 

.38 

20.00 

1.97 

5.20 

1 

.51 

26.67 

2.28 

6.00 

IX 

.63 

33.33 

2.57 

6.80 

A                       -03 

1.58 

.84 

4.20 

X 

.06 

3.33 

1.08 

5.40 

X 

.13 

6.67 

1.54 

7.70 

X 

.19 

10.00 

1.89 

9.50 

X 

.25 

13.33 

2.20 

11.00 

% 

.31 

16.67 

2.45 

12.20 

% 

.38 

20.00 

269 

13.40 

'• 

i 

When  the  natural  grade  of  the  land  is  so  steep  as  to 
make  it  dangerous  to  employ  ditches  of  the  same  grade, 
suitable  drops  must  be  installed  at  various  points.  (Figs. 
135, 136.)  To  carry  water  from  the  laterals  to  furrows,  in 


434 


IRRIGATION  PRACTICE 


FIG.  152.  Utah  lay-off  and  pulverizer. 

soils  that  "wash"  easily,  lath  boxes,  already  mentioned, 
or  pipes  are  often  used.  (Fig.  137,  138.) 

In  constructing  ditches  it  is  usually  sufficient  to  step 
off  the  distances,  and  any  simple  leveling  device  gives  the 
necessary  levels.  (Fig.  139.) 

255.  Gates  and  checks. — Gates  for  the  admission  of 
water  from  the  supply  ditches  into  the  laterals  may  be 


FiQ.  153.  Robinson's  adjustable  corrugator  and  renovator. 


IRRIGATION  TOOLS  AND  DEVICES 


435 


made  in  almost  any 
way  to  suit  the  farmer, 
from  a  simple  board, 
removed  when  the 
flow  is  desired,  to 
elaborate  doors 
hoisted  by  machinery. 
In  ordinary  farm 
practice,  permanent 
plain  wooden  or  con- 
crete frames  into 
which  the  gate  may 
be  dropped  constitute 
the  most  effective 
device  (Fie  140  )  FlG' 155'  Ridger  in  check  and  basin  irrigation- 
To  guide  the  water  from  the  lateral  ditches  on  to  the 
land,  devices  to  check  or  dam  the  flow  are  employed.  The 


FIG.  154.  Ridger  in  check  and  basin  irriga  ion. 


FIG.  156.  Furrower  in  action. 


FIG.  157.  Cultivator. 


FIG.  158.  Cultivator  attachments. 
(436) 


IRRIGATION  TOOLS  AND  DEVICES 


437 


most  common  check  is  a  shovelful  of  dirt  placed  in  the 
ditch  at  the  point  where  the  division  of  water  is  desired. 
At  times  the  checks  are  made  by  a  dammer,  while  the 
ditch  is  dry-  before  the  irrigation.  The  dirt  check  is  only 
temporary,  is  often  washed  away,  and  involves  consider- 
able labor.  A  portable  wooden  dam  or  check,  or  dam 
made  of  a  board  with  one  or  more  holes  in  it,  which  can 


FIG.  159.  Beet  cultivator  attachments. 

be  inserted  wherever  needed  and  removed  at  will,  has 
been  found  very  satisfactory.  The  metal  dam  or  tappoon 
has  also  given  satisfaction.  The  canvas  dam  has  of  recent 
years  been  extensively  adopted,  and  is  said  to  be  of 
especial  value  because  it  may  be  made  to  fit  the  ditch 
snugly.  It  is  held  down  by  a  shovelful  of  dirt,  so  that  it 
is  really  a  modification  of  the  original  dirt  check.  The 


438 


IRRIGATION  PRACTICE 


FIG.  160.  Cutaway  disk  harrow. 

canvas  dam  is  made  of  a  piece  of  strong  canvas,  nailed 
firmly  to  a  wooden  cross  piece.  At  times  there  is  an  open- 
ing in  it  to  divide  the  irrigation  stream.  Sometimes  a 
small  obstruction  such  as  a  submerged  flashboard  or  a 
lath  dropped  across  the  bottom  of  the  ditch  is  sufficient 
to  divert  the  water  into  the  lateral.  (Figs.  141-150.) 


FIG.  161.  Clod  crusher,  pulverizer,  leveler  and  smoother. 


IRRIGATION  TOOLS  AND  DEVICES 


439 


FIQ.  162.  Frieze  water  register. 


256.  Ridging   and   furrowing. — The 

field-ditch  method  of  irrigation  requires 
only  that  a  few  rather  small  furrows 
may  be  made  to  assist  in  guiding  the 
water  over  the  land.  These  furrows  are 
ordinarily  made  by  the  point  of  the 
hoe  or  as  a  very  shallow  plow  furrow. 
The  check,  border  and  basin  methods 
of  irrigation  require  that  ridges  or 
levees  be  thrown  up  around  the  plots. 
For  this  purpose  any  of  the  ordinary 
farm  implements  may  be  employed, 
although  special  "ridgers"  and  "crowd- 
ers"  are  made  and  used  on  many 
farms. 

The  furrow  system  of  irrigation 
requires  that  parallel,  uniform  furrows 
be  made  for  guiding  the  water  over  the 
land.  These  may  be  made  by  hand  with  a  hoe,  but  only 
with  great  labor.  Numerous  devices  have  been  proposed 
for  making  uniform  furrows  with  horse  labor.  The  shovel 
attachment  to  the  cultivator  has  been  used,  but  with 


440 


IRRIGATION  PRACTICE 


indifferent  success,  because  the  furrows  were  not  left 
smooth.  One  of  the  first  devices  of  the  Utah  pioneers 
was  a  large  roller  with  several  wooden  "shoes"  each  one 

of  which  made  a  fur- 
row. (Fig.  151.)  This 
gave  excellent  satis- 
faction except  that 
the  rolling  of  the  land 
made  rapid  evapora- 
tion possible.  From 
this  implement  has 
developed  the  Utah 
layoff  and  pulverizer 
(Fig.  152),  especially 
adapted  for  alfalfa  fields.  The  furrows  are  cut,  the  clods 
pulverized  and  the  smoothed  ground  mulched  by  a  rear 
attachment  of  spike  teeth.  Many  other  devices  for  fur- 
rowing have  been  made.  (Figs.  153-156.) 

257.  Mulching  the  soil. — Well-cultivated  soils  produce 
crops  with  the  least  expenditure  of  water.  Implements  for 
cultivation  are  therefore  of  the  highest  importance  to  the 
farmer.  Such  implements  are  now  on  the  market  in  great 


FIG.  163.  Device  for  measuring  miner's  inches. 


FIG.  164.  Cross  section  of  canal  for  measurement  of  flow. 

numbers.  Clods  may  be  broken  by  the  corrugated  roller; 
the  alfalfa  fields  disked  by  the  disk  with  jagged  cutting 
edges;  the  mulch  may  be  made  by  one  of  the  tooth  harrows, 
the  disk-harrow  or  any  one  of  the  many  available  culti- 


IRRIGATION  TOOLS  AND  DEVICES 


441 


vators.  The  main  thing  is  to  fit  the  tool  to  the  crop  and 
the  soil.  Particularly  important  is  the  soil.  Most  harrows 
and  cultivators  are  now  so  built  that  different  kinds  of 
teeth  and  shovels  may  be  attached;  thereby  a  much  larger 
field  of  service  is  possible.  (Figs.  157-161.) 

258.  Measuring  the  flow  of  water. — Brief  consider- 
ation of  this  subject  has  been  given  hi  Chapter  XVII. 


FIG.  165.  Current  meters. 

Special  engineering  treatises  should  be  consulted  for  more 
information.  All  in  all,  some  form  of  the  weir  is  the  best 
measuring  device  on  the  farm.  It  often  becomes  desirable 
for  the  farmer  to  keep  a  constant  record  of  the  water 
flowing  over  a  weir.  To  do  this,  automatic  registers  con- 
nected with  floats,  and  run  by  clockwork,  have  been 
devised.  The  rising  and  falling  of  the  float,  indicating  the 


442 


IRRIGATION  PRACTICE 


rise  and  fall  of  the  water,  is  registered  on  a  record  sheet 
that  may  be  preserved  for  future  use.    (Fig.  162.) 

Where  miners'  inches  are  units  of  measurement,  de- 
vices like  that  of  Fig.  163  are  used.  The  United  States 
Geological  Survey  makes  a  cross-section  of  a  canal  or 
river  at  a  given  point  (Fig.  164)  and  determines  the  velocity 
of  the  flow  there,  with  current  meters.  (Fig.  165.)  Many 


FIG.  16  6.  Grant-Mitchell  meter. 

special  measuring  devices  are  also  available,  as  the  Grant- 
Mitchell  meter.  (Fig.  166.) 

Similarly,  a  great  number  of  water  divisors,  in  addition 
to  those  mentioned  in  Chapter  XVII,  have  been  tried 
out  with  varying  success. 

A  very  great  amount  of  work  has  been  done  by  engi- 
neers on  the  measurement  of  flowing  water.  The  results 
obtained  are  of  high  practical  value.  It  must  be  said, 
however,  that  the  engineers,  themselves,  have  not  as  yet 
agreed  upon  the  measuring  device  best  suited  to  the  use 
of  the  farmer.  Engineering  books  should  be  consulted 
for  further  information  on  this  subject. 


444  IRRIGATION  PRACTICE 


REFERENCES 

FORTIER,  SAMUEL.  Practical  Information  for  Beginners  in  Irriga- 
tion United  States  Department  of  Agriculture,  Farmers' 
Bulletin  No.  263  (1906). 

JOHNSTON,  C.  T.,  and  STANNARD,  J.  D.  How  to  Build  Small  Irri- 
gation Ditches.  United  States  Department  of  Agriculture, 
Farmers'  Bulletin  No.  158  (1902). 

TEELE,  R.  P.  Preparing  Land  for  Irrigation.  United  States  Depart- 
ment of  Agriculture,  Yearbook  for  1903. 

WIDTSOE,  J.  A.  Dry-Farming.  Chapter  XV.  The  Macmillan  Com- 
pany (1911). 


CHAPTER  XXI 
THE  HISTORY  OF  IRRIGATION 

THE  history  of  irrigation  is  full  of  interest,  for  it  is 
virtually  the  story  of  the  most  progressive  peoples  of 
historical  times.  Like  all  human  history,  it  is  fragmentary 
and  can  be  pieced  together  only  by  much  labor.  The 
history  of  irrigation  is  yet  to  be  written;  this  chapter  is 
but  a  brief  and  incomplete  sketch  of  the  subject. 

259.  The  antiquity  of  irrigation. — The  practice  of 
irrigation  antedates  recorded  history  in  every  great  coun- 
try of  antiquity.  Whether  it  originated  in  Asia,  Africa, 
Europe  or  America,  no  man  can  tell.  Beyond  question, 
where  man  first  appeared,  there,  not  long  after,  irrigation 
began  to  be  practised.  Together  with  the  stirring  of  the 
soil  and  the  sowing  of  seed,  irrigation  is  one  of  the  first 
agricultural  practices  of  mankind. 

The  monuments  of  Egypt  declare  that  Menes,  the 
first  king  of  the  first  dynasty,  extended  greatly  the  irri- 
gation structures  of  his  day.  How  long  before  him,  in  the 
unrecorded  past,  irrigation  had  been  practised  in  Egypt, 
is  not  known.  Certain  it  is,  however,  that  in  the  succession 
of  dynasties,  throughout  the  glory  of  Egypt,  even  to  the 
present  humble  day,  the  waters  of  the  Nile,  used  in  irri- 
gation, have  made  of  Egypt  a  granary  of  food.  In  the 
days  of  Joseph,  the  son  of  Jacob,  "all  countries"  came  to 
Egypt  for  food. 

The  monuments  of  Babylon  and  Assyria  declare  with 
equal  emphasis  that  irrigation  was  a  full-grown  practice 

(445) 


446  IRRIGATION  PRACTICE 

on  the  vast  Mesopotamian  plains,  when  the  first  records 
were  laid  aside  for  our  use  in  the  latest  day.  Hammurabi, 
a  contemporary  of  Abraham,  built  a  great  and  wonderful 
canal  by  which  the  desert  was  made  into  gardens,  and  an 
elaborate  system  of  irrigation  covered  the  Babylonian 
plain,  under  which  grain  returned  300-fold.  These  mighty 
structures  fell  into  disuse  and  decay  as  the  power  of  the 


FIG.  168.  Sagebrush  land. 

ruling  nation  receded  from  Babylon,  but  the  remains  of 
the  canals  are  visible  today,  and  the  fertile  soil  is  as  ready 
as  ever  to  respond  to  the  touch  of  water.  Moreover,  the 
recently  unearthed  codes  of  laws  concerning  the  use  of 
irrigation  water  prove  a  degree  of  irrigation  refinement 
scarcely  ever  surpassed. 

In  Persia,  India,  Ceylon,  China,  Syria,  Palestine,  and 
practically  every  country  of  high  antiquity,  irrigation  has 
been  practised,  without  cessation,  since  the  beginnings  of 


THE  HISTORY  OF  IRRIGATION 


447 


history.  It  is  unquestioned  that  in  Egypt  and  the  Asiatic 
countries  the  practice  of  irrigation  goes  back  2,000  years, 
and  it  may  be  4,000  years. 

On  the  American  continent,  also,  the  practice  of  irri- 
gation goes  back  to  immemorial  times.  At  the  time  of 
the  Spanish  Conquest,  irrigation  practice  was  found  well 
developed,  and  irrigation  structures  existed  then  which 
dated  back  to  the  first  traditions  of  the  native  population. 
In  Peru  are  remains  of  irrigation  structures  of  undoubted 
antiquity  and  of  a  quality  comparable  with  the  best  of 


FIG.  169.  The  Boon. 


the  present  day.  In  Chile,  similar  remains  are  found.  In 
Argentina,  there  are  remains  of  vast  irrigation  structures. 
In  fact,  along  the  Atlantic  and  Pacific  drainages  of  South 
America,  wherever  the  climate  made  it  desirable,  great 
irrigation  structures  were  built  in  a  remote  antiquity. 
In  some  places  stupendous  irrigation  canals  may  be 
traced — 400  to  500  miles  long — far  beyond  our  modern 
attempts.  There  is  evidence  to  show,  also,  that  on  the 
American  continent  refinements  of  irrigation  were  prac- 
tised, superior  to  any  others  known. 


448 


IRRIGATION  PRACTICE 


FIG.  170.  Shadof  of  Egypt  or  paecottah  of  India. 

Likewise,  in  Mexico  and  the  southwestern  United 
States  are  remains  of  prehistoric  canals,  which  prove 
amply  the  high  antiquity  of  irrigation  in  North  America. 
To  the  past  belongs  the  credit  of  having  originated  irri- 
gation; our  present  day  must  refine  it  and  make  it  im- 
perishable. 


THE  HISTORY  OF  IRRIGATION  449 

260.  The  Christian  era,  to  1800. — Clearly,  a  valuable 
practice  so  ancient  and  so  widespread,  as  is  irrigation, 
could  not  vanish  from  the  earth.  Therefore,  in  spite  of 
the  changing  fortunes  of  the  race  which  has  covered  but 
a  small  part  of  the  earth,  irrigation  has  remained  a  con- 
tinuous practice.  In  some  places,  as  in  Babylon,  with  the 
decline  in  civilization  and  the  diminution  of  population, 
irrigation  disappeared  wholly  or  in  part;  while  in  other 
places,  as  in  Egypt,  China  and  Persia,  it  has  continued 
and  often  increased.  New  countries  have  adopted  it;  and 
most  of  the  older  ones  have  maintained  it.  The  most 
enlightened  peoples  have  always  practised  and  do  now 
practice  irrigation,  if  the  climatic  conditions  make  it 
desirable.  It  is  difficult  for  an  unintelligent  or  shiftless 
people  to  become  good  irrigators. 

During  the  Christian  era,  the  practice  of  irrigation 
has  moved  westward,  with  the  general  western  movement 
of  civilization.  During  the  days  of  the  Roman  Empire, 
irrigation  was  fostered  in  all  the  Mediterranean  countries, 
although  relatively  few  remains  of  the  Roman  structures 
are  known.  That  it  was  of  high  importance  in  Roman 
days  is  well  shown  by  the  attention  given  irrigation  in 
the  famous  codes  of  law  formulated  in  the  fifth  and  sixth 
centuries  after  Christ.  As  another  trifling  but  interesting 
evidence,  Carpenter  gives  the  word  "rivals,"  derived  from 
"rivus,"  an  artificial  water  channel,  or  ditch.  The  users 
from  a  "rivus"  were  rivals — the  usual  contests  over  water 
are  clearly  implied. 

The  invasion  of  southern  Europe  by  the  Moors,  hi  the 
ninth  and  tenth  centuries  after  Christ,  became  a  great 
stimulus  to  irrigation.  The  Moorish  conquerors  had  a 
good  traditional  and  practical  knowledge  of  irrigation, 
and  sensed  quickly  the  value,  to  southern  Europe,  of  more 
cc 


450  IRRIGATION  PRACTICE 

extensive  irrigation.  Therefore,  during  their  rule,  especially 
in  Spain,  many  large  canals  were  built,  and  irrigation 
practices  perfected.  To  Roman  and  Moorish  rule,  together, 
must  be  ascribed  the  beginnings  of  many  of  the  splendid 
irrigation  structures  of  France,  Spain  and  Italy. 

In  France,  irrigation  has  been  practised  under  a  great 
variety  of  conditions.  The  first  great  canal  in  France, 
the  St.  Julien,  seems  to  date  from  about  1171.  Other  and 
minor  structures  were  built  in  the  centuries  that  followed, 
up  to  1800  A.  D. 

Spain,  among  the  countries  of  southern  Europe,  has 
most  need  of  irrigation,  and  many  of  her  smaller  irrigation 
canals  date  back  to  Roman  times.  After  the  Moorish 
occupation,  from  the  eleventh  to  the  thirteenth  centuries, 
particularly  in  the  valley  of  the  Genii,  in  Granada,  many 
great  canals  were  built,  which  have  endured  to  the  present 
time.  The  delivery  of  water  was  so  greatly  perfected  in 
those  days  that  the  Valencia  Canal,  for  instance,  has  been 
managed  for  600  years  with  the  laws  that  now  prevail. 
From  the  thirteenth  century,  onward,  there  was  some 
added  irrigation  development  under  many  of  the  enlight- 
ened rulers  of  Spain.  The  modern  irrigation  activity 
began  in  Spain  as  early  as  1759,  earlier  than  in  any  other 
land. 

Italian  irrigation  has  grown  so  steadily  and  intelli- 
gently from  the  eleventh  to  the  nineteenth  centuries  that 
Italy  has  been  denominated  the  classic  land  of  irrigation. 
In  the  eleventh  century,  the  old  Roman  canals  in  Lom- 
bardy  were  reconstructed.  In  Italy,  the  twelfth  century 
was  marked  by  tremendous  irrigation  activity.  The 
thirteenth,  fourteenth,  fifteenth  and  sixteenth  centuries 
all  contributed  largely  to  irrigation  development,  and  the 
canals  then  built  are  now  in  service.  In  the  seventeenth 


THE  HISTORY  OF  IRRIGATION  451 

century,  under  the  domination  of  Spain,  the  proper  details 
of  irrigation  practice  were  vigorously  promoted  and  some 
canals  were  built.  During  the  eighteenth  century,  few 
large  additions  were  made  to  the  irrigation  system  of 
Italy,  but  the  existing  canals  were  used  diligently. 

After  the  discovery  of  America,  the  zealous  Catholic 
missionaries  established  missions  hi  various  parts  of  the 
two  American  continents.  These  priests  were  chiefly  from 
southern  Europe  and  well  acquainted  with  irrigation. 
Whenever  a  mission  was  established  in  an  arid  section,  a 
small  irrigation  system  was  also  built  for  the  support  of 
the  mission.  The  remains  of  these  mission  irrigation 
systems  are  found  in  various  parts  of  America,  notably 
in  California.  In  a  few  cases,  also,  the  Catholic  fathers 
taught  the  natives  irrigation,  or  rather  insisted  upon  the 
use  of  the  ancient  knowledge.  The  Catholic  missionaries 
did  not  succeed  in  establishing  American  irrigation  on  a 
community  scale,  beyond  that  already  existing  among  the 
aborigines. 

During  the  first  1,800  years  of  the  Christian  era,  the 
irrigated  countries  of  antiquity  continued  their  irrigation 
practices;  the  countries  of  Europe,  particularly  France, 
Spain  and  Italy,  adopted  and  extended  the  practice  greatly, 
and  the  new  lands  brought  under  the  domination  of  civi- 
lized man  made  little  or  no  irrigation  progress. 

261.  Irrigation  in  recent  times. — The  new  light  of 
advancing  science  finally  showed  the  great  nations  of 
the  nineteenth  century  that  irrigation  is  a  great  world 
problem.  Even  hi  the  countries  of  southern  Europe,  in 
which  irrigation  had  developed  under  the  influence  of  a 
growing  civilization,  new  structures  were  planned  and 
completed,  methods  of  practice  perfected  and  more  intelli- 
gent laws  enacted.  In  France,  since  about  1839,  many 


452  IRRIGATION  PRACTICE 

large  canals  have  been  constructed;  in  Spain,  also,  much 
irrigation  progress  has  taken  place  during  the  nineteenth 
century,  and  in  Italy  the  Great  Cavour  Canal  was  built 
about  1844,  with  minor  ones  since  that  date,  and  in  1865 
the  valuable  irrigation  code  of  Victor  Emmanuel  was 
promulgated. 

The  greatest  recent  progress  in  irrigation  has  occurred, 
chiefly,  under  Anglo-Saxon  direction  in  newly  settled 
countries  or  in  older  settled  countries  brought  under 
Anglo-Saxon  rule. 

Thus,  in  Egypt,  under  English  rule,  with  the  wise 
initiative  of  Mehemet  Ali  Pasha  in  1820,  an  irrigation 
revival  has  begun  which  promises  to  eclipse  in  its  results 
the  noonday  of  ancient  Egyptian  irrigation.  The  old 
channels  have  been  deepened  and  extended,  new  and  more 
economical  methods  of  irrigation  have  been  adopted,  new 
and  profitable  crops  have  been  introduced,  and,  as  the 
climax,  the  great  Assuan  Dam  has  been  built  as  the  first 
main  step  toward  utilizing  the  varying  flow  of  the  Nile 
in  an  unvarying  manner.  True,  while  this  revival  began 
early  in  the  nineteenth  century,  it  was  only  in  the  last 
quarter  of  the  century  that  the  really  big  things  in  recent 
Egyptian  irrigation  have  been  done. 

India,  under  English  rule,  is  likewise  in  an  irrigation 
development  far  beyond  the  greatest  in  the  history  of  this 
age-old  land.  From  immemorial  times  droughts,  with 
consequently  fearful  famines,  have  vexed  India.  Early  in 
the  nineteenth  century,  the  rulers  began  to  look  to  an 
extended  irrigation  for  relief  from  famine.  The  year 
1878,  at  the  end  of  a  disastrous  famine,  may  be  said  to  be 
the  beginning  of  modern  irrigation  in  India.  Commissions 
were  appointed,  new  canals  constructed  and  great  efforts 
made  to  establish  a  large  and  thoroughly  modern  irrigation 


THE  HISTORY  OF  IRRIGATION  453 

system.  As  a  result  of  these  activities,  the  irrigated  area 
of  India  was  increased,  between  1877  and  1897,  from  6 
per  cent  to  7.5  per  cent  of  all  the  arable  land.  Irrigation 
development  in  some  phase  is  being  pushed  with  un- 
diminished  vigor. 

South  Africa  has  also  shared  in  the  recent  irrigation 
development.  Cape  Colony,  ceded  to  England  in  1814, 
began  its  recent  growth  with  the  diamond  discoveries  of 
1870.  Soon  afterwards,  in  1877,  irrigation  boards  were 
organized  to  consider  the  small  and  scattered  irrigation 
efforts  of  the  past  and  to  propose  new  and  greater  plans 
which  have  been  in  part  carried  out.  Since  1904,  in  the 
other  states  of  British  South  Africa,  irrigation  develop- 
ment has  been  undertaken  on  a  large  scale.  In  fact,  so 
urgent  had  the  interest  in  irrigation  become  that,  in 
1909,  an  irrigation  congress  was  held  for  all  British  South 
Africa.  Much  irrigation  progress  may  be  looked  for  hi 
South  Africa. 

Australian  irrigation  has  had  a  similar  history.  Iso- 
lated irrigation  plants  were  established  soon  after  the 
settlement  of  the  continent,  but  it  was  only  in  1884  that 
a  royal  commission  was  appointed  to  consider  ways  and 
means  of  irrigation  development.  Since  1885  govern- 
mental consideration  has  been  given  to  irrigation  with  the 
result  that  notable  structures  have  been  built  and  much 
advance  made  in  the  reclamation  of  the  arid  lands. 

In  many  other  countries,  on  all  the  continents,  interest 
in  irrigation  has  been  developed  in  recent  years,  and  in 
many  of  them  irrigation  dams  and  canals  have  been 
constructed.  Argentina,  for  example,  although  only  at  the 
threshold  of  her  agricultural  development,  has  already 
constructed  several  irrigation  works  of  considerable 
extent. 


454  IRRIGATION  PRACTICE 

The  greatest  recent  progress  in  irrigation  has  come 
about  in  every  country  during  the  last  forty  or  fifty  years. 
The  year  1880  may  well  be  taken  as  a  convenient  marker 
for  the  beginning  of  modern  irrigation  on  a  large  scale, 
with  governmental  support  and  based  upon  modern 
knowledge. 

262.  The  founding  of  modern  irrigation  in  America. — 
During  the  first  half  of  the  nineteenth  century,  there  was 
no  irrigation  progress  in  America.  The  native  Indians 
in  some  few  places  in  Mexico  and  South  America,  were 
irrigating  small  fields.  The  old  missions  in  the  United 
States  were  falling  into  decay.  The  European  conquerors 
of  the  new  continent  were  busily  engaged  in  the  humid 
portions  of  the  country.  The  more  arid  or  remoter  pans 
of  the  country  had  been  explored  only  by  the  handful  of 
trappers  and  a  few  others,  who  had  ventured  westward 
largely  in  search  of  adventure  or  scientific  truth.  The 
great  territory  now  covered  by  the  mountain  states  was 
designated  on  the  school  maps  as  the  Great  American 
Desert,  and  with  the  country  adjoining  it  on  every  side, 
was  held  to  be  unfit  for  agricultural  purposes. 

The  opening  of  the  Oregon  country  brought  venture- 
some settlers  across  the  continent  more  frequently,  until 
the  old  Oregon  trail  was  pretty  well  defined,  but  those 
who  traveled  it  sought  their  homes  on  the  Pacific  Coast, 
where  the  rainfall  was  quite  as  heavy  as  in  the  far  East. 
The  old  southwest  trail  from  Santa  Fe  was  practically 
unused  by  emigrants.  There  was  no  American  irrigation 
of  any  consequence  during  the  first  half  of  the  nineteenth 
century. 

Early  in  the  spring  of  1847,  a  party  of  pioneers,  under 
the  leadership  of  Brigham  Young,  set  out  from  their 
winter  camp,  near  what  is  now  Council  Bluffs,  to  find  in 


THE  HISTORY  OF  IRRIGATION 


455 


the  far  West  a  place  where  their  people  could  settle.  On 
July  24,  1847,  this  party  of  pioneers  entered  the  Great 
Salt  Lake  Valley,  chosen  as  the  place  of  settlement,  and 
on  that  day  planted  potatoes  hi  what  is  now  the  business 
section  of  Salt  Lake  City,  and  gave  the  soil  a  "good 
soaking"  of  water  brought  from  the  neighboring  City 
Creek  through  a  plow  furrow  that  served  as  a  ditch. 
This  was  the  birth  of  modern  irrigation  in  America. 


~ 


FIG.  171.  Caravan  crossing  the  plains  in  early  irrigation  days. 

The  Mormon  pioneers  possess  the  honor  of  having 
founded  modern  irrigation  in  America,  not  because  of  the 
initial  irrigation  on  July  24, 1847,  but  because  the  Mormon 
people  continued  the  work,  dug  extensive  canals,  brought 
thousands  of  acres  under  irrigation,  devised  methods  of 
irrigation,  established  laws,  rules  and  usages  for  the 
government  of  populous  settlements  living  "under  the 
ditch," — hi  short,  because  they  developed  permanent 
irrigation  agriculture  on  a  community  scale,  under  the 


456  IRRIGATION  PRACTICE 

conditions  and  with  the  knowledge  of  modern  civilization. 
Irrigation  knowledge  and  inspiration  have  been  drawn 
by  the  whole  world  from  the  work  of  the  first  American 
irrigation  pioneers. 

The  far-reaching  consequences  of  this  original  experi- 
ment resulted  from  a  combination  of  conditions  not 
before  known  in  irrigation  history.  The  pioneers  settled 
in  the  very  heart  of  the  arid  section  at  a  time  when  the 
nearest  settlements  to  the  east  or  to  the  west  were  1,000 
miles  away.  Starvation  or  successful  agriculture  was  the 
only  alternative  offered,  since  a  return  to  civilization  was 
almost  impossible  to  the  weary  people  with  worn-out 
equipment.  They  were  compelled  to  make  irrigation 
successful.  Then,  they  were  wholly  unfamiliar  with 
irrigation  practices.  True,  they  were  men  and  women  of 
good  intelligence  and  information,  and  knew  the  place  of 
irrigation  in  the  world's  history;  some  of  them  also  had 
probably  seen,  in  their  native  New  England,  the  occa- 
sional irrigated  meadow;  but,  they  had  no  real  knowledge 
of  irrigation  as  the  central  idea  of  agriculture.  They 
were,  therefore,  unhampered  by  traditional  irrigation 
practices,  and  built  from  the  foundation  as  their  needs 
and  intelligence  directed.  Moreover,  these  irrigation 
pioneers  were  of  the  race  that  had  carried  onward  modern 
civilization;  of  a  country  with  huge  courage  to  achieve 
great  tasks,  and  of  a  day  when  new  and  increasing  truth 
rendered  easier  the  work  of  man.  They  founded  their  irri- 
gation, therefore,  in  vision  and  with  modern  intelligence. 
Naturally,  under  such  conditions,  the  system  of  irrigation 
that  arose  in  the  heart  of  the  Great  American  Desert  was 
modern  and  original  in  method  and  application,  and  be- 
came a  system  to  which  modern  man,  interested  in  the 
conquest  of  the  desert,  has  since  looked  for  help. 


THE  HISTORY  OF  IRRIGATION  457 

263.  The  growth  of  American  irrigation. — The  original 
irrigation  pioneers  of  July  24,  1847,  numbered  147;  in  1865, 
nearly  64,000  souls  were  living  in  Utah  and  were  deriving 
their  main  sustenance  from  irrigation.  During  these 
eighteen  years  more  than  1,000  miles  of  irrigation  canals 
had  been  constructed,  another  500  miles  were  being 
dug,  and  154,000  acres  of  cultivated  land  were  under 
irrigation. 

In  1865  the  average  acre-yield  of  wheat  was  23  bushels; 
of  barley,  30  bushels;  of  oats,  31  bushels;  of  corn,  20  bush- 
els; of  potatoes,  139  bushels;  of  beets,  265  "bushels;"  of 
carrots,  344  "bushels;"  of  meadow  hay,  l%tons;  of  cotton, 
151  pounds;  and  of  sorghum,  79  gallons.  Considering 
that  the  rapidly  arriving  farmers  had  to  be  taught  irri- 
gation, and  were  provided  with  poor  machinery,  these 
yields  showed  the  great  possibilities  of  irrigation. 

Soon  after  the  founding  of  irrigation  in  the  Great  Salt 
Lake  Valley,  gold  was  discovered  in  California.  Most  of 
the  tens  of  thousands  who  flocked  to  the  gold-fields  passed 
through  Utah  and  Salt  Lake  City  and  thus  became  in  a 
measure  acquainted  with  irrigation.  Many  of  these 
emigrants,  upon  their  arrival  in  California,  found  irrigation 
agriculture  more  profitable  than  gold-hunting.  Others, 
rich  or  discouraged,  returned  to  their  homes  in  the  East, 
and  told  not  only  of  the  gold-fields,  but  of  the  conversion 
of  the  heartless  desert  into  a  fruitful  garden  by  the  intelli- 
gent will  of  a  courageous  people.  The  stories  of  the  trav- 
elers gained  currency  until  the  whole  country  knew  a  little 
of  the  practice  and  possibilities  of  irrigation  in  the  Great 
West.  Moreover,  big-visioned  men,  like  Major  J.  W. 
Powell,  and  his  great  associates  on  the  United  States 
Geological  Survey  who  had  explored  the  arid  region,  or 
like  Horace  Greeley,  who  had  carefully  informed  himself, 


458  IRRIGATION  PRACTICE 

spoke  and  wrote  of  the  great  opportunities  of  the  West 
under  irrigation. 

However,  the  year  1870  was  almost  reached  before 
the  American  people  began  to  give  serious  attention  to  the 
irrigable  West,  so  strange  and  forbidding  did  irrigation 
seem  to  the  rainfall  farmers.  With  the  opening  of  the 
;70's  came  a  slight  change  of  heart.  Many  colonies  were 
established,  and  with  every  year  the  emigration  increased. 
In  1878,  Major  J.  W.  Powell's  report  on  the  arid  lands  was 
published  by  the  government.  The  public  interest  became 
aroused.  The  westward  movement  was  already  covering 
the. Great  Plains,  and  overflowing  steadily  into  the  region 
where  irrigation  was  at  that  time  generally  held  to  be 
indispensable.  All  classes  of  people  discussed  the  Great 
West  as  a  great  hope  of  the  Republic. 

From  1870  to  1880,  the  population  of  the  mountain 
states  doubled;  from  1880  to  1890,  it  almost  doubled 
again.  The  future  of  irrigation  was  safe.  Then,  the  cau- 
tious men  of  money  thought  their  opportunity  had  come. 
Great  sums  were  spent  in  building  splendid  canals  above 
fertile  lands,  with  the  thought  that  the  farmers  who  settled 
below  the  canal  would  pay  a  royal  annual  tribute  for  the 
water  delivered  to  the  land.  But  the  process  of  settling 
a  new  country  is  slow;  irrigation  succeeds  best  under  a 
close  social  and  economic  organization  in  which  canal- 
owner  and  water-user  must  be  equal  members,  and  the 
West  is  large;  so,  in  face  of  the  slow  adjusting  of  difficulties 
and  the  slower  settlement  of  the  projects,  capital  often 
became  discouraged  and  surrendered  its  property  at  a  loss 
rather  than  to  await  the  sure  harvest  that  the  years  would 
bring.  Occasionally,  also,  as  in  all  enterprises,  the  careless 
or  dishonest  or  ignorant  speculator  appeared  and  for  a 
time  misled  both  capital  and  farmer. 


460  IRRIGATION  PRACTICE 

Soon  after  1890,  the  era  of  the  irrigation  speculator 
ended.  The  development  of  irrigation  continued  un- 
diminished,  but  along  safe  and  legitimate  lines.  Legis- 
lation by  state  and  federal  governments  (such  as  the 
Carey  Act)  encouraged  sane  irrigation  progress.  Western 
Canada,  lying  under  the  same  general  conditions  as 
western  United  States,  joined  vigorously  in  the  movement, 
constructed  canals  and  opened  fertile  lands  for  settlement. 
Finally,  the  greatest  irrigation  experiment  of  modern 
days  was  officially  declared  successful  when  the  Congress 
of  the  United  States  in  1902  passed  the  great  reclamation 
act. 

The  irrigation  structures  existing  in  the  United  States 
in  1910  irrigated  nearly  14,000,000  acres,  and  could  irri- 
gate nearly  20,000,000  acres.  All  this  has  been  done 
since  1847;  and  the  work,  still  going  on,  is  far  from 
being  finished. 

264.  The  Union  Colony  of  Colorado. — This  colony, 
which  in  1870  founded  Greeley,  Colorado,  is  next  to  the 
Utah  settlement  the  most  important  in  the  history  of 
American  irrigation,  for  it  also  established  the  practice 
on  a  community  scale  and  demonstrated  the  essential 
correctness  of  the  methods  of  the  Utah  pioneers.  The 
colony  was  organized  on  the  cooperative  plan  by  N.  C. 
Meeker,  who  had  earlier  in  life  belonged  to  cooperative 
settlements  and  who  had  also  become  familiar  with  the 
Utah  method  of  settlement.  The  members  of  the  enter- 
prise were  men  and  women  of  a  high  order  of  intelligence 
and  ideals,  who  carried  onward  the  cooperative  spirit. 
The  early  success  of  the  colony,  upon  which  the  later 
success  rests  firmly,  may  be  credited  to  the  union  feature. 
It  has  been  observed  that  all  irrigation  enterprises  in 
which  many  families  draw  support  from  one  ditch  or 


THE  HISTORY  OF  IRRIGATION  461 

system  of  ditches  become  more  successful  as  the  coope- 
rative spirit  grows.  Other  colonies  were  soon  founded 
near  and  in  imitation  of  the  Union  Colony,  as,  for  instance, 
the  Chicago  Colony  at  Longmont,  the  Fountain  Colony 
at  Colorado  Springs,  the  Agricultural  Colony  at  Fort 
Collins,  and  the  Southwestern  Colony  at  Green  City. 
The  work  of  these  colonies  helped  to  place  on  a  sounder 
basis  the  practice  of  irrigation  in  the  United  States,  and 
made  of  northeastern  Colorado  one  of  the  most  famous 
agricultural  districts  of  the  country. 

The  Union  Colony,  with  its  outgrowths,  is  entitled  to 
the  credit  of  being  associated  with  the  first  serious  at- 
tempts to  measure  and  distribute  water  accurately  for 
irrigation.  In  this  part  of  Colorado,  also,  were  suggested 
and  initiated  many  of  the  systematic  investigations  of  the 
conditions  determining  successful  irrigation.  Many  famous 
names  are  connected  with  the  struggles  of  the  Colorado 
irrigation  pioneers,  originating  with  the  Union  Colony  of 
1870.  The  Colorado  experiments  confirmed  the  Utah 
experience. 

265.  The  United  States  Reclamation  Service. — During 
the  first  fifty  years  of  irrigation  in  the  United  States,  the 
Federal  government  gave  little  direct  assistance  to  the 
reclamation  of  arid  lands  beyond  the  enactment  of  laws 
that  made  the  public  domain  readily  available  to  the 
settler.  As  the  public  lands  under  large  rainfall  passed 
into  private  ownership,  and  the  demand  for  homesteads 
continued,  Congress  gave  consideration  to  federal  aid  to 
irrigation,  and  on  June  17,  1902,  nearly  fifty-five  years 
after  the  founding  of  modern  American  irrigation,  passed 
the  justly  famous  reclamation  act. 

This  act  provides  that  all  moneys  received  from  the 
sale  and  disposal  of  public  lands  in  all  the  states  west  of 


462  IRRIGATION  PRACTICE 

and  including  North  and  South  Dakota,  Kansas  and 
Oklahoma,  excepting  the  5  per  cent  set  aside  for  educa- 
tional purposes,  shall  be  made  a  "reclamation  fund"  for 
the  "examination  and  survey  for  and  the  construction 
and  maintenance  of  irrigation  works  for  the  storage,  di- 
vision, and  development  of  waters  for  the  reclamation  of 
arid  and  semi-arid  land  in  the  said  states."  The  lands 
brought  under  irrigation  by  this  act  shall  be  open  to 
bona-fide  settlers  under  the  regulations  of  the  Secretary 
of  the  Interior,  and  at  a  price  that  will  return  in  time  to 
the  reclamation  fund  a  sum  equal  to  that  expended  by 
the  government  upon  the  project.  The  fund,  thus  made 
permanent,  may  continue  to  serve  until  all  irrigation 
projects  feasible  under  the  terms  of  the  act  shall  have 
been  constructed. 

Work  under  the  reclamation  act  has  been  pushed 
with  vigor  almost  from  the  day  the  act  was  signed  by 
Theodore  Roosevelt.  The  workers  have  been  assembled 
under  the  head  of  the  United  States  Reclamation  Service, 
the  director  of  which  almost  from  the  beginning  has  been 
F.  H.  Newell,  a  life-long  student  of  water  supply  and 
irrigation,  assisted  by  a  most  admirable  and  efficient  corps 
of  irrigation  experts.  During  its  first  decade  of  work, 
the  Reclamation  Service  undertook  projects  which,  when 
completed,  will  cost  over  $100,000,000.  In  1910  the  pro- 
jects of  the  Reclamation  Service  irrigated  3  per  cent  of 
all  the  irrigated  lands  in  the  country,  and,  when  completed, 
would  irrigate  nearly  7  per  cent  of  the  area  to  be  irrigated 
under  all  projects,  private  and  public. 

Many  projects  that  private  enterprise  felt  unable  to 
undertake  have  been  constructed  by  the  Reclamation 
Service.  Confidence  in  the  arid  section  has  been  strength- 
ened by  the  national  approval  of  irrigation  contained  in 


THE  HISTORY  OF  IRRIGATION  463 

the  reclamation  act.  The  real  problems  and  possibilities 
of  irrigation  are  being  brought  home  to  our  national 
leaders  by  this  work  as  would  be  possible  in  no  other  way. 
It  is  a  great  act  of  endless  service  to  the  country.- 


FIG.  173.  Major  J.  W.  Powell,  who,  as  director  of  the 
United  States  Geological  and  Geographical  Surveys, 
was  one  of  the  first  to  understand  and  teach  the  value 
of  the  arid  and  semi-arid  parts  of  the  United  States. 

It  was  fitting  that  the  Interior  Department  should  be 
entrusted  with  the  execution  of  the  reclamation  act,  for 
it  was  the  Geological  Survey  that  among  government 
agencies  first  studied  the  beginnings  of  irrigation  in  the 
far  West,  and  spoke  hopefully  of  the  reclamation  of  the 


464  IRRIGATION  PRACTICE 

Great  American  Desert.  Major  J.  W.  Powell,  Director  of 
the  United  States  Geological  and  Geographical  Surveys, 
and  lover  of  the  West,  together  with  G.  K.  Gilbert  and 
other  colleagues,  did  much  to  advance  the  early  cause  of 
irrigation.  Under  the  direction  of  the  Geological  Survey, 
also,  with  F.  H.  Newell  as  hydrographer,  the  notable 
water-supply  papers  were  issued  which  laid  a  foundation 
of  knowledge  concerning  stream  flow  upon  which  irri- 
gation plans  could  be  builded. 

266.  The  United  States  Department  of  Agriculture. — 
The  building  of  dams  and  canals  will  end,  but  the  use  of 
the  impounded  or  diverted  water  must  go  on  forever. 
Irrigation  is  essentially  an  agricultural  practice  to  which 
the  civil  and  mechanical  engineers  can  give  only  initial 
help.  In  the  earlier  days  water  was  plentiful  and  people 
few,  and  little  water  scarcity  was  felt.  The  big  thing  was 
to  dig  more  canals  and  induce  more  people  to  settle  under 
the  ditch.  Now,  the  question  of  the  best  use  of  the  water 
on  the  land  is  the  big  one,  because  the  opportunities  are 
fewer,  the  people  more  numerous,  and  those  of  the  arid 
region  more  determined  to  build  permanently  and  largely. 
The  Department  of  Agriculture,  although  somewhat  slow 
in  sensing  the  needs  of  the  irrigation  farmers,  organized 
in  1898  the  Irrigation  Investigations  of  the  Office  of  Experi- 
ment Stations,  to  expend  a  Congressional  appropriation 
"for  the  purpose  of  collecting  from  agricultural  colleges, 
agricultural  experiment  stations,  and  other  sources, 
valuable  information  and  data  on  the  subject  of  irrigation 
and  publishing  the  same  in  bulletin  form."  Elwood 
Mead,  already  of  long  and  splendid  irrigation  service, 
was  first  appointed  chief  of  the  Investigations,  followed  in 
1906  by  Samuel  Fortier,  also  with  a  long  and  honorable 
irrigation  record.  In  a  short  time,  a  series  of  remarkable 


466  IRRIGATION  PRACTICE 

irrigation  bulletins  appeared,  which  have  continued  to 
the  present.  Doctors  Mead  and  Fortier  gathered  about 
themselves  a  body  of  young  able  men,  who  for  half  a 
generation  have  been  devoting  themselves  to  a  study  of 
the  farmers7  side  of  irrigation.  The  practices  of  irrigation 
have  been  collected  and  organized;  the  irrigation  systems 
of  foreign  countries  have  been  studied;  experiments  have 
been  conducted,  and  in  numerous  ways  the  irrigation 


FIG.  175.  Steam  power  digs  the  modern  canals. 


farmer  has  been  given  needed  help.  Not  the  least  of  the 
achievements  of  the  United  States  Irrigation  Investi- 
gations has  been  the  encouragement  it  has  given  irrigation 
studies  at  the  experiment  stations  by  an  intelligent  and 
liberal  system  of  cooperative  work. 

267.  The  experiment  stations. — Modern  agriculture 
was  founded  in  humid  regions  and,  naturally,  little 
attention  was  at  first  given  irrigation.  When,  however, 
in  1887,  an  agricultural  experiment  station  was  established 
in  each  of  the  states  and  territories,  irrigation  problems 
presented  themselves  for  solution  at  most  of  the  western 
stations.  E.  W.  Hilgard,  the  great  man  of  arid  agri- 


468 


IRRIGATION  PRACTICE 


culture,  had  already  made  observations  on  Californian 
irrigation  for  half  a  generation,  but  his  fundamental  soil 
studies  had  crowded  out  systematic  irrigation  experi- 
ments. 

The  Colorado  and  Utah  stations  were  the  first  to 
undertake  special  irrigation  work.  At  the  Colorado  Station, 
among  the  many  workers  who  gave  some  attention 


FIG.  177.  Dam  of  Salmon  River  project,  Idaho,  built  by  private  enterprise. 

to  irrigation,  Elwood  Mead  and,  later  and  chiefly,  L.  G. 
Carpenter,  made  classical  studies  of  the  measurement, 
division,  seepage  and  underflow  of  water,  together  with 
many  allied  questions.  True  to  its  traditional  interest  in 
the  engineering  phases  of  irrigation,  the  Colorado  Station, 
in  cooperation  with  the  United  States  Irrigation  Investi- 
gations, completed  in  1913  an  experimental  plant  for  the 
study  of  the  methods  for  measuring  and  dividing  water, 
which  is  unequaled.  At  the  Utah  Station,  J.  W.  Sanborn, 


THE  HISTORY  OF  IRRIGATION 


469 


a  great  pioneer  of  modern  American  agriculture,  assisted 
by  Mills,  inaugurated  the  pioneer  investigations  of  the 
correct  use  of  water  on  the  farm.  J.  A.  Widtsoe,  L.  A. 
Merrill  and  others  later  organized  the  exhaustive  study  of 
the  relationships  existing  between  soils,  crops  and  water, 
having  for  its  purpose  the  determination  of  the  most 
economical  use  of  water,  which,  in  new  hands,  is  still 
being  continued.  The  Utah  experimental  equipment  for 


FIG.  178.  Plant  for  the  study  of  the  measurement  and  division  of  water.    The 
Colorado  Experiment  Station. 

these  investigations  was  long  unique  among  the  stations. 
At  the  Utah  Station,  Samuel  Fortier  also  did  some  of  his 
early  experimental  work,  and  many  members  of  the  station 
staff  have  conducted  investigations  bearing  more  or  less 
directly  on  irrigation. 

The  other  western  stations  have  all  done  some  excellent 
irrigation  work;  but  the  preponderance  has  been  on  the 
subject  of  alkali,  rather  than  on  the  actual  use  of  water  on 
the  farm.  E.  B.  Voorhees,  of  the  New  Jersey  Station, 
studied  with  care  the  value  of  irrigation  in  humid  countries. 


470  IRRIGATION  PRACTICE 

The  experiment  stations  have  brought  forth  much 
new  irrigation  knowledge,  and  have  disseminated  widely 
all  the  sound  information  existing  upon  the  subject. 
Nearly  all  the  stations  in  the  arid  region  are  now  under- 
taking systematic  studies  having  for  their  purpose  the 
establishment  of  a  science  of  irrigation  practice. 

268.  The  Irrigation  Congress. — The  reclamation  act, 
the  land  laws  making  irrigation  settlement  possible,  the 
founding  and  work  of  the  experiment  stations,  are  all  the 
result  of  the  championship  of  irrigation  by  clear-headed, 
far-seeing,  courageous  men,  in  and  out  of  office,  who,  in 
legislative  halls,  from  the  platform,  on  the  printed  page 
and  in  private  conversation,  have  taught  the  needs  and 
the  possible  future  of  irrigation  in  America. 

These  men,  whose  names  are  easily  forgotten,  now  that 
the  work  is  done,  organized  in  Salt  Lake  City  the  Irrigation 
Congress.  The  first  session  was  held  in  September,  1891, 
since  when  sessions  have  been  held  in  practically  all  of  the 
irrigation  states.  Its  lists  of  officers  during  these  many 
years  include  the  names  of  the  irrigation  leaders  of  America 
— names  of  national  renown  for  great  service  rendered. 
The  proceedings  of  the  Congress  developed  and  sustained 
the  enthusiasm  which  has  made  irrigation  a  national 
issue.  No  doubt  the  Irrigation  Congress  made  possible 
much  of  our  recent  irrigation  progress.  Now  that  reser- 
voirs and  canals  are  being  rapidly  built  and  irrigation  has 
been  firmly  established,  the  mission  of  the  Congress  looms 
larger  than  ever — to  make  systematic,  profitable  and  per- 
manent the  use  of  the  water  upon  the  land. 

Major  Richard  W.  Young,  a  grandson  of  the  founder 
of  modern  irrigation  in  America,  is  the  present  President 
of  the  Irrigation  Congress.  The  Congress  for  1914  will  be 
held  in  the  province  of  Alberta,  Canada. 


THE  HISTORY  OF  IRRIGATION  471 


REFERENCES 

POWELL,  J.  W.,  with  GILBERT,  G.  C.,  BUTTON,  C.  E.,  and  THOMP- 
SON, A.  H.  The  Lands  of  the  Arid  Region  of  the  United  States. 
United  States  Department  of  the  Interior  (1878). 

UNITED  STATES  DEPARTMENT  OF  STATE.  Canals  and  Irrigation  in 
Foreign  Countries.  Special  Consular  Reports,  Vol.  V  (1898). 

GRAY,  E.  D.  MCQUEEN.  Government  Reclamation  Work  in  Foreign 
Countries.  United  States  Government  Printing  Office  (1909). 


CHAPTER  XXII 

PERMANENT  AGRICULTURE  UNDER 
IRRIGATION 

"THE  desert  shall  blossom  as  the  rose,"  said  the 
ancient  prophet;  and  a  modern  man,  witnessing  the  ful- 
fillment, by  irrigation,  of  the  ancient  prediction,  was  so 
wrought  upon  by  the  transformation  of  desert  into  garden 
that  he  declared  it  a  miracle.  Later,  another  man,  per- 
ceiving clearly  the  permanency  of  the  work,  declared  that 
irrigation  is  a  continuous  miracle.  That  was  nearer  the 
truth.  Today,  with  our  greater  understanding,  irrigation 
is  less  of  a  miracle;  it  is  more  of  an  intelligent  conquest — • 
a  continuous  conquest  of  the  untoward  forces  of  the  desert. 

269.  The  big  irrigation  problem. — The  word  "con- 
tinuous," whether  it  be  of  miracle  or  of  conquest,  lingers, 
for  it  expresses  the  essence  of  the  virtue  of  irrigation. 
The  mountain  stream  or  the  sluggish  river,  once  brought 
through  reservoir  and  canal  upon  the  desert  land,  will 
make  that  land  yield  in  plenty  and  in  beauty,  not  for  a 
generation  or  two,  but,  if  man  so  decrees,  during  the 
coming  ages  of  the  earth — at  least  while  climatic  con- 
ditions remain  unchanged.  Therefore  is  the  builder  of 
the  irrigation  canal  a  master-builder. 

The  battle  for  recognition  has  been  fought  and  won. 
Arid  and  humid  regions  look  to  irrigation  as  one  of  the 
chief  weapons  with  which  to  conquer  drought  and  to 
make  the  land  yield  richly.  Private  capital  and  public 
funds  vie  with  each  other  for  the  privilege  of  fostering 

(472) 


AGRICULTURE  UNDER  IRRIGATION  473 

irrigation.  It  seems  certain  that  as  soon  as  sound  growth 
will  allow  all  the  water,  especially  in  the  arid  regions,  will 
be  stored  and  diverted  for  purposes  of  irrigation. 

The  mighty  dams  and  endless  lines  of  canals  will  soon 
be  completed.  If  the  work  has  been  well  done,  we  shall 
need  only  to  maintain  in  a  sound  condition  the  structures 
of  steel  and  rock  and  cement  and  wood  and  earth  that 
have  been  built.  The  overshadowing  problem  then,  as  it 
is  the  great  one  now,  will  be  that  of  using  the  water  in 
the  best  manner  for  the  production  of  crops.  Two- 
headed  is  this  problem:  First,  the  water  must  be  made  to 
produce  the  largest  total  yield  of  crops  for  the  support  of 
man;  second,  the  practice  of  irrigation  on  a  given  area  of 
land  must  be  made  continuous  and  increasingly  desirable. 
To  this  double  problem  is  this  volume  devoted. 

270.  The  spirit  of  irrigation. — Our  modern  knowledge 
is  teaching  the  methods  whereby  irrigation  may  be  made 
to  produce  the  maximum  crops  for  each  unit  of  water  used. 
All  irrigation  advocates  are  rapidly  accepting  the  new 
truth.    The  very  spirit  of  the  conquest  of  the  desert  is 
that  men  shall  be  benefited — many  men;  the  more  men 
the  better.    The  largest  possible  area  of  land  must  be 
reclaimed  by  the  stored  waters,  even  if  the  acre-yield 
does  not  reach  so  high  an  average. 

271.  No  essential  difference  between  irrigation-  and 
humid-farming. — Our   modern    knowledge    teaches    also 
that  there   is  no   essential   difference   between  rainfall- 
farming  and  irrigation-farming,  except  in  the  manner  in 
which  water  is  applied  to  the  soil.   Every  argument  against 
the    permanency   of    irrigation-farming   may   be    urged 
against  rainfall-farming;  and  every  argument  for  the  per- 
manency of  rainfall-farming  may  be  used  with  equal  force 
in  behalf  of  irrigation-farming.    The  everlasting  relation- 


474  IRRIGATION  PRACTICE 

ships  among  soils,  waters  and  plants  are  the  same  over  all 
the  earth.  Under  irrigation,  the  great  water  factor  may 
be  controlled,  and  thereby  greater  power  for  good  or  for 
evil  is  possessed  by  the  farmer  under  the  ditch. 

Yet  there  are  some  who,  while  admitting  the  great 
present  value  of  irrigation,  fear  that  in  it  is  an  element  of 
weakness  which  will  make  the  practice  temporary. 

272.  History   assures   permanence   of   irrigation. — A 
sufficient  answer  may  be  the  history  of  the  past.  As  shown 
in  the  preceding  chapter,  great  tracts  of  lands  are  known 
that  have  been  farmed  successfully,  under  irrigation,  dur- 
ing the  last  2,000  to  4,000  years  and  are  today  as  pro- 
ductive as  ever.    In  fact,  the  human  race  was  cradled  and 
grew  to  maturity  in  irrigated  countries.    That  some  of 
the  great  nations  of  antiquity  crumbled  to  dust  was  not 
because  they  dwelt  on  irrigated  lands;  their  fall  was 
rather  delayed  because  of  the  bounteous  yields  of  their 
irrigated  fields;  and,  in  truth,  the  fallen  nations  of  the 
past  practised  irrigation  for  so  long — often  for  thousands 
of  years — that  the  permanent  nature  of  this  branch  of 
agriculture  was  well   demonstrated   before  the  shifting 
scenes  of  history  brought  new  lands  and  other  peoples 
into  emphatic  view. 

273.  The  question  of  plant-food.— The  fertility  of  the 
soils  must  be  carefully  guarded  under  irrigation  as  under 
rainfall.    When  moderate  quantities  of  water  are  used  no 
more  plant-foods  are  washed  away  than  under  an  equiva- 
lent rainfall.    Instead,  the  deep,  rich  soils  of  the  arid  re- 
gions, because  of  the  possible  water  storage  in  them,  can 
better  retain  the  essential  elements  of  plant-food.   During 
the  course  of  modern  American  irrigation,  extending  over 
two-thirds  of  a  century,  the  average  productive  power  of 
the  irrigated  lands  has  steadily  increased.    Against  the 


AGRICULTURE  UNDER  IRRIGATION 


475 


FIG.  179.  Work  for  a  man.    Irrigation  requires  strength  of  body,  good  intelligence 
and  sound  and  rapid  judgment. 

fifteen  or  twenty  bushels  of  wheat  per  acre  harvested  in  the 
first  years  of  irrigation,  forty  to  fifty  bushels  are  now 
harvested  on  the  same  lands.  True,  this  must  be  due 
chiefly  to  improved  methods  of  culture,  with  modern 
tools,  but  certainly  there  is  in  this  record  no  sign  of 
deterioration. 


476  IRRIGATION  PRACTICE 

274.  Some  advantages  of  irrigation. — There  are  many 
reasons  why  irrigation-farming  should  become  and  remain 
very  attractive.     Under  irrigation,  crop-yields  may  be 
depended  on  from  year  to  year.    Crop  failures  are  very 
rare  and  are  usually  due  to  hail-storms  or  some  unusual 
atmospheric  disturbances.    The  possibility  of  varying  the 
quantity  of  water  applied  to  the  land  gives  the  farmer  a 
control  over  the  yield  and  quality  of  the  crop  that  does 
much  to  vitalize  the  routine  of  the  work  and  to  make  the 
harvest  more  profitable.    The  soil  and  climatic  conditions 
prevailing  over  most  of  the  territory  demanding  irrigation 
are  of  a  kind  to  make  life  enjoyable. 

275.  Finally. — The  nature  of  irrigation  is  such  as  to 
bring  into  close  social  relationship  the  people  living  under 
the  same  canal.   A  common  interest  binds  them  together. 
If  the  canal  breaks  or  water  is  misused,  the  danger  is  for 
all.    In  the  distribution  of  the  water  in  the  hot  summer 
months  when  the  flow  is  small  and  the  need  great,  the 
neighbor  and  his  rights  loom  large,  and  men  must  gird 
themselves  with  the  golden  rule.    The  intensive  culture, 
which  must  prevail  under  irrigation,  makes  possible  close 
settlements,  often  with  the  village  as  a  center.    Out  of 
the  desert,  as  the  canals  are  dug,  will  come  great  results 
of  successful  experiments  in  intimate  rural  life;  and  out 
of  the  communities  reared  under  irrigation  will  come  men 
who,  confident  that  it  is  best,  can  unflinchingly  consider 
their  neighbors'  interests  with  their  own;  and  who,  there- 
fore, can  assume  leadership  in  the  advancing  of  a  civili- 
zation based  upon  order  and  equal  rights. 

The  environment  of  wise  irrigation-farming  compels 
the  belief  that  of  all  kinds  of  farming  it  may  be  the  most 
enduring. 

KING,  F.  H.   Farmers  of  Forty  Centuries  (1911). 


APPENDIX  A 
WATER  CONSTANTS 

Chemical  formula  for  water =H2O. 

Specific  gravity  of  water  =  1. 

Maximum  density  of  water  occurs  at  4°  C.  or  39.2°  F. 

1  cubic  foot  of  water  at  4°  C.  =62.2786  pounds. 
1  cubic  foot  of  water  at  49°  F.  =62.2515  pounds. 
1  gallon  (U.  S.)  of  water  =  8.3254  pounds. 
1  cubic  foot  of  water  =  7.48  gallons. 
1  litre  of  water =2. 1997  pounds. 
1  ton  =  32.1  cubic  feet  of  water. 

1  acre-foot  =  the  volume  of  water  which  will  cover  an  acre  1  foot  deep. 
1  acre-inch  =  the  volume  of  water  will  cover  an  acre  1  inch  deep. 
1  acre-foot  =  43, 560  cubic  feet. 
1  acre-foot  =  2,712,856  pounds. 

1  California  "miner's  inch"  =0.020  cubic  feet  per  second. 
1  Colorado  "miner's  inch"  =0.026  cubic  feet  per  second. 
1  Arizona  "miner's  inch"  =0.025  cubic  feet  per  second. 

1  cusec  =  1  second-foot  =  1  cubic  foot  of  water  per  second. 

1  second-foot  flowing  for  twenty-four  hours  (=86,400  cubic  feet) 
will  cover  1  acre  1.9835  feet  deep  =  1.9835  acre-feet  (approxi- 
mately 2  feet). 

1  second-foot  flowing  for  120  days  will  cover: 

240  acres  1  foot  deep.  120  acres  2  feet  deep. 

180  acres  \Y^  feet  deep.  80  acres  3  feet  deep. 


(477) 


c^oicoco'co     -<j5  TJ!  -«t  TJ!  ic     ic'iccoco'co 


JOOOCOCO          iCCOt^OSrH  Tj<r^rHCOrH          CO  N  OS  CO  CO 

!_<•,_;  rH  rH          (N  M  (N  <N  CO         CO  CO  CO  CO*  TJ?          TjH  -rJH  Tj<  1C  1C 


(NiOCCi 

OiO—  i 


ioilN        (N(N(NdcO       COCOCOCO-* 


M 

M 


& 


OrH<Nco»c     cqt>-ooosi 

^  ,_;  ,.;  ^  ^4          rH  rH  rH  rH  ^          (N  (N  N  <N  (N 


OSCOCOrHGO        CD-^COINO        OOS05XOO        OS  OS  O  O -H 

rficcot^t^     oqosOrHiN     cocoTjHicco     r>.oqqrH(N 

'^rn'rH          rtrHrHrHrH          rH  rH  (N  M  N 


iMOO        iCfOOGO»0        CO<NO03t^        CO  lO  »O  Tt<  Tj< 

CO  CO        t-OOOSOSO       i—  1  (M  CO  00  Tt*        iOCOI>OOOS 


OSCO        ^C<1OOOCO 
^iM        CO  •<*  1C  1C  CO 


rHlCO3Tt«O5 


ICOOOHCOS       COt^rHCOO        iCOS^OSTt*        OSrt*O>CrH 

<N  N  co  co  co     T^^ICICCO     eqcot^t^oq     oqosqqrH 


QOrHTt<COO5         (MlCOSIMlC         O5(NCOOSCO         t>.rHlCO5CO 
rH  (N  IN  (N  (N        CO  CO  CO  •*  Tjn        T)H  1C  1C  1C  CO        CO  t~-  1>  t>;  GO 


COOGOCOCO          COCOb-CSrH  Tft^rHCOrH  CO  (N  OS  CO  CO 

(N^JfiCr^OS        rHCOiCt^-O        (N^t-»OS(M        TfH^OSiNiC 

^H  ,_!  rH  rH  rH          (N  (N  (N  M  CO          CO  CO  CO  CO  T}<          •*  Tj<  T}<  »C  1C 


£i 


IM  CO         CO 


(478> 


•r- 


CO 

«    w 

lor 
3  I 

s  s 

II 


8  i  •£ 

50  £ 

I  .a 

1 

I 

o  1  ^ 

'  I 

O  £ 


fij    1 

U     tc 

«     § 

11 

i| 
II 


oocJcidd     d-5>-H<N<N     eo  &•<?•<{  10 


-i  C5t-.«3tOtO  10  COt- 00  O  COCOQCO 
r>.  OrtJOOINCO  O^«C^t>.  i-HiOO^ 
o6  C5  OS°  OS  O  O  ri  *4  »*  fit  0^  tt 


^osoot^r- 
o       coo  os 


tttooo     0  os  os  os 


CO-*<OCO«) 

oq  i-j  •*  <q  os 
t^i>     1^06060606 


ci  « ec  co  co' 


>Tf<        CDt-OSi-HC 


dOOiO^HOO  "5C<IOt>->O 
Ti4  tO  t-;  O>  O  N  •*  CO  t>;  CS 
TJ4  TJ4*  TJ4'  TJ4  »O  IO  IO  tO*  1C  IO 


1-1  co  10  oo  1-1  -*t^ocot~ 
osqi-jw^j  locooqcsq 
cicocococo  coco'coco-^5 


COCOCOTj<Tj(        COiOtOt-OO       Cii-HNTf<C 
Oi-KNCOTjj       lOOt-OOOS       OfNCO-^i 

CNC4CicNc4       CO  CO*  CO  CO  CO       CO  CO  CO*  •*'  rji 


i-3  ,-H  ,-H  <N  <N       CNCNCICNci       CN(NCNC<JCQ       CO  CO  CO  COCO 


c4e4c«eie4 


t^^H^OiO       Ci^QOCOOO 

oos  Oi-ii-4(NCN 


^HMTC-^iO       Ol^OOOSO       i-HNCOTt«»O        CO  t*  00  OS  O 
CO  CO  CO  CO  CO        CO  CO  CO  CO-*        •*  TlJ  TJH  -^  -^       •^•^•41  ^<  to 


(479) 


1 


I -a 

fi      H*3 
O      X° 

«   « 

pf  w 

|   or 

•a   £ 

s  1 

II 


O  | 

§  S 

§  § 

H  'C 


Ml! 

in 


CCCCTTjH       U5COCOI> 
<N(N(N<N(N       <N<N<N<N( 


D  00  Oi  O  O       »-H  i—  5  C*4 


WOC<1^00      >-<»COU5 

tccSS     (NooSS 


(NINiNCCM 


i?3cqc^ 


oooooodd     ddrH^rt' 

(NMC 


CCMCCPO 
OCOCOO5I 


O^HOOOt--       »O  •rf  Tt<  CC  N       N  N  M  N  C<1       MMTjflfSCO       t^XOC^ 
COIOCOOO       o'<N-<f<COOO       O<N-*OOO       O<N4<«O»       OC^»Ot>. 

o«dcDco«o     t>t^i>t>^     0006060606     oioJoioJd 


O       (Nt^MOSCO       iMOiiOlNOi       «OCOO^»O 
TjdOOOOO       (NCOiOt^OO       O(N^iOt>- 

fioioio'id     ic»C"5Oco     «codto't>I     i>t^t^i>t^     0606060606 


^TfTt-^io     ^iioiowjio     io»o'»ocdco     ooddcd     t>^t^t^t>t^ 


OOO5O'-lN 

cor^o>o.-i 


COCCOOCCCO       COC«3C«3CCCO       T^T)!-^-^-*       Tji^' 


ro  oo  co  0  co     c«  co  co  cc 


r4  ^  i-«  ei  <N'     IN  N*  <N  <N  <N 


t^OO  00 


lOiOiO'O'O       iCiOiCiO«O       O5OCOCOCO       CD^O«Ot>; 


(480) 


9  Ss  3!  io  8    o  o  o  § ! 


|g   S33! 


1 


11 


D  us  •*  co  eo     co  •*  •*  IQ  r-     oo  c  JO  «a : 

r^oooooid     d'-H'-icioi     co  TjJ  ^  10  >o     oi^t^oooo     o3dd'-H( 
MC^MC^JO     cororcccw     cococococo     cococcwro     «•*•<}<•*• 


^ 

3  3 

2  g 

8  I 

*  w 


u 


i-t  »O  OS  «J(  O5 


S3S58 

N       ?3<NlNC>4N       (N^S^?5 


i-Ot^O<N"D       t^OCOOOS       COOOCOlN.       i-H 
rHCOOMO       (NiOt^OJr-t       ^i»O5»-iCO 


H     J3 

6  * 


>         02 
°         g 

H    T 

O      c3 

i^0 

S  ^ 


»-H  CO  C^  Is—  CO       C5  *O  I-H  Is- CO       O  *Q  CO  C5  O       CO  O  Is-  ^  *"•*       00  O  CO  ^  30 

r^t^oooooo     oooooooioJ     cscicicicS     co'ddcJ     ^^^H'^-;^ 


O«O5O<N       COiOOt^OS       OINCOTjiO       t^OOC<ICO       OOWOSi-< 

^t^     t^t^t^t^t^     0600060606     oooooioJos 


LOiOiOiCSO       0«50«CCO       «<0501>t>: 


t>:  06  06  06  06 


rfTf-^TfTj;        TfiOiOiCiO        IQ  iQ  1Q  iQ  iO 


(481) 


19 

o    ^ 
5    w^ 

CO 

pr  fo 
|a 

J     JS 

0  I 

il 


e  s 

OJ  g 

5  rf 

O  § 

H  •§ 

1^ 

S  i§ 

fi 


§    Sb 


jUSfe 


^HiO  00  CO  t>.  N  GO      ^»-i 

.^^  ^icio  to 

O.-H<N'  w 

i~-t^t^-  t- 


SSSSc?    S! 


>O       ^OO 
"5       C4  00  > 


Tj>CiOc          COI>t 
WCOMCOCO       CCCOM 


>o»ocDt>      rtooooo       os  o  cs  c  1-      >-  »- 

(NININININ       <N(NIM(M<N        (N  (M  m  CO  CO       CO  00 


GOGOOOCROJ     oJoiddd     ,-5  ,-5 


00  lO  CO  i-t  < 

ioooS  ^ 

,-5  1-5  <N'  ejeeeoeo 

(NiN<N  O4C^C^W<N 


COQOCSfN-* 


>OCOXO5i-i       MrJ<CDXO       <NiOb»C5(N 

t>-  os  r-i  cc         oo  q  c<  ^  i>     as  i-j  ec  10  oo 
t^i>r^i>     i>o6o6o6oo 


COCOCOCO        00  CO  • 


<N'  pi  oi  co  oo     oo  oo  oooo 


Tt*t^OCOCO        OSlNiOOOi-l        •*  GO  i-H  rf<  00       IM  1C  OS  CO  «O 

oocoododos     osos'ososcs     oioJddd     ddddi-5 


^(NCO^iO 

O  O  O  O  O 


00  00 


t>-GOC5O       T-il 


X  OS  O       1-1  CSI 


(482) 


1 

•3 -a 
§3 

CO 

af  co 


1 1 

I* 

a  A 

*2    "^ 

2  § 

a  1 

SI       O 
K     — 

§      § 


|     > 

B      o 


§    3, 

N|l 

K 


S'^HIN'CO       Tfic^tvlx       oic'O'-<N 
XXX       X  X  X  X  X       X  OS  C:  55  35 


^-i^t^OM        «O5fOt^-H        IOC5«OC«        OOWOOMO        •*  O  CO  ( 
t>i-nOO^t«        OOC^Jl^^O        OrfOlCCOO        Nt-i-iOO       «CO-^ 


-HCS»«»O  Tjnroc^i^o  OC5050SX  xxoiosos  OQ-<MN 

X  O  CC  O  Ci  C^l  iO  X  »— *  ^  Is-  O  M  iC  X  i-^  ^  t^*  O  CO  t^"  O  CO  sO  O^ 

CO  ^  ^  Tt«  T}<  1C  ifs  iC  CO  O  CO  SO  t^  t^-  Is-  00  X  OO  C5  C5  O5  O  O  O  O 

C<JNC^NC^  WCS|C<IC<IC^  C<INC^C<1CN«  N  M  C>J  C<l  C<>  C<J?OCOCCCO 


ooqooiTjj     o(35^Hco»o     r-o^coio     t^CNT^s 

00  00  OS  C5  OS        OS  OS  C  C5  C5 


t^     ^xodod 


(483) 


APPENDIX  C 

The  following  brief  list  gives  the  titles  of  the  few  books  on  irri- 
gation for  the  farmer  published  in  the  United  States: 
ANDERSON,  D.  H.    Primer  of  Irrigation.    D.  H.  Anderson  Publish- 
ing Company,  Chicago  (1903). 

BOWIE,  A.  J.    Practical    Irrigation.     McGraw    Publishing    Com- 
pany (1908). 
KING.  F.  H.    Irrigation  and  Drainage.    The  Macmillan  Company, 

New  York  (1899). 
MEAD,  ELWOOD.   Irrigation  Institutions.  The  Macmillan  Company, 

New  York  (1903). 

NEWELL,  F.  H.   Irrigation.  T.  Y.  Crowell  &  Co.,  New  York  (1902). 
OLIN,  W.  H.  American  Irrigation  Farming.   A.  C.  McClurg  &  Co., 

Chicago  (1913). 
SMYTHE,  W.  E.    The  Conquest  of  Arid  America.    The  Macmillan 

Company,  New  York  (1905). 
STEWART,  HENRY.    Irrigation  in  Field  and  Garden.    Orange  Judd 

Company,  New  York  (1886). 

WILCOX,  Lucius  M.    Irrigation  Farming.    Orange  Judd  Company, 
New  York  (1902). 


(484) 


INDEX 


Abraham,  446. 

Absolute  duty  of  water,  335. 

Absorption  by  soils,  76. 

of  water  by  roots,  109, 

effect  of  initial  percentage,  111. 
Adams,  368,  369. 
Advantage  of  irrigation,  476. 
Africa,  duty  of  water  in,  338. 

use  of  saline  water  in,  387. 
Agricultural  Colony,  461. 
Alfalfa,  152. 

See  also  Lucern. 

time  of  watering,  186. 

protein  in,  221. 

yield  due  .to  rainfall,  234. 

under  irrigation,  266. 

cultivation  of,  268. 

method  of  irrigation,  269. 

time  of  irrigation,  270. 

quantity  of  water  for,  274. 

duty  of  water,  344. 
Alfalfa  seed,  277. 
Algeria,  83. 

Alkali.     See    also    Over-irrigation    and 
Seepage,  371. 

drainage  from  a  soil,  78. 

upward  leaching,  81. 

use  of  concentrated  water,  89. 

defined,  383. 

and  seepage,  384. 

upward  leaching,  385. 

use  of  saline  water,  387. 

deposits,  388. 

kinds,  390. 

white,  brown  and  black,  392. 

plant  tolerance  for,  392. 

tolerance  of  various  plants,  394. 

tolerance    according    to    Bureau    of 
Soils,  395. 

cropping  against,  397. 

chemical  treatment  for,  398. 

tillage  against,  399. 

scraping  against,  399. 

washing  out,  400. 

drainage,  the  remedy,  400. 
Almonds,  spacing  of,  317. 
Alway,  39. 


Amazon,  84. 

America,  founding  of  modern  irrigation, 

454. 

Ames,  Iowa,  407. 
Anderson,  405. 
Anderson,  D.H.,  484. 
Anglo-Saxon  irrigation,  452. 
Apples,  protein  in,  221. 

duty  of  water  for,  322. 

sugar  in,  225. 

spacing,  317. 

Application,  distribution  on,  364. 
Apricots,  spacing,  317. 
Argentina,  453. 
Arizona  Station,  179. 
Arkansas  River,  83. 
Artesian  water,  410. 
Ash  constituents.    See  also  Plant-food 

in  plants,  219. 
Asia,  duty  of  water  in,  339. 
Asparagus,  under  irrigation,  309. 
Assam,  India,  rainfall  at,  2. 
Assimilation  of  carbon  by  plants,  128, 

129. 

Assuan,  338,  452. 
Assyria,  445. 
Atlanta,  408. 

Attraction  of  near  bodies,  8. 
Australia,  453. 

duty  of  water  expression,  331. 

duty  of  water  in,  343. 
Australian    saltbush,    alkali -resistant, 
397. 

Babylon,  445. 

Bacteria,  soil,  and  water,  104. 

Bark,  234,  248,  249,  264,  273,  284,  345, 

369. 
Barley,  under  irrigation,  255. 

duty  of  water,  344. 

alkali-resistant,  396. 

in  humid  climates,  411. 

early  yield,  457. 
Barri-Doab  Canal,  341. 
Bartlett,  405. 
Basin  irrigation,  207. 
Beans  under  irrigation,  301. 


(485) 


486 


INDEX 


Bear  River,  83. 

Bear  River  Canal,  duty  of  water,  253, 

344. 

Beckett,  63,  215. 
Beets,  early  yield,  457. 
Bell,  106. 

Belle  Fourche  River,  96. 
Belz,  44,  63. 
Bennett,  329. 
Bighorn  River,  96. 
Billings,  Mont.,  78. 

alkali  experiment,  402. 
Blackberries,  326. 

protein  in,  221. 

sugar  in,  225. 

in  humid  climates,  410. 
Bond,  264. 
Bonsteel,  403. 
Border  irrigation,  202. 
Bouyoucos,  118,  125,  156. 
Bowie,  409,  417,  484. 
Breaking  land,  419. 
Briggs,  20,  44,  63,  126,  156. 
Brome-grass,  278. 
Brown,  403. 
Buckingham,  51,  52, 63. 
Buckley,  340,  369. 
Buds  affected  by  irrigation,  320. 
Buergerstein,  126. 
Burke,  403,  405. 
Burr,  39. 

Cabbage  under  irrigation,  308. 
Cache  la  Poudre  River,  83. 
California,  457. 

flooding  irrigation  in,  315. 

duty  of  water  in,  323. 

lined  ditches  in,  378. 

rivers,  84. 

California  station,  15,  30. 
Cameron,  48,  63,  66,  68,  70,  106,  387, 

392. 

Campbell,  62,  239. 
Canals,  loss  from  Indian,  341. 

seepage  from,  371. 
Cantaloupe,  171. 

under  irrigation,  306. 
Canvas  dam,  438. 
Canada,  460. 

rivers,  85. 

duty  of  water  expression,  331. 

irrigation  in,  339. 
Cape  Colony,  339,  453. 
Capillarity.     See  Soil   moisture,  Soils, 
Water. 

maximum  capacity,  17. 
Carbohydrates  in  plants,  224 


Carbon,   assimilation   by   plants,    128, 

129. 

Carey  Act,  460. 
Carpenter,  352,  369,  372,  374,  403,  449, 

468. 
Carrots,  time  of  irrigation,  185. 

under  irrigation,  296. 

early  yield,  457. 
Catholic  Fathers,  451. 
Cauliflower  under  irrigation,  308. 
Cavour  Canal,  452. 
Celery  under  irrigation,  309. 
Cement  concrete,  as  ditch-lining,  377. 
Cereals,  irrigation  of,  240. 
Ceylon,  446. 
Chalis  River,  83. 
Check  irrigation,  202. 
Checks  for  ditches,  434. 
Cherries,  protein  in,  221. 

sugar  in,  225. 

spacing,  317. 
Chicago  Colony,  461. 
Chili,  447. 

duty  of  water  in,  342. 
China,  416,  446. 
Cincinnati,  408. 
Cippoletti's  weir,  352.    See  also  Wen. 

discharge  over,  478. 
Citrus  trees  under  irrigation,  321. 

duty  of  water  for,  322. 

water  requirements,  323. 
Clark,  39,  312. 
Clarke,  83,  90,  106. 
Clearing  land,  419. 
Clover,  red,  under  irrigation,  281. 

in  humid  climates,  411. 
Coburn,  284. 
Coit,  312,  327,  329. 
Collins,  106. 
Color  of  plants,  227. 
Colorado,  time  of  irrigation  in,  320. 

alkali  from,  391. 
Colorado  River,  96. 
Colorado  Station,  355,  468. 
Colorado  Springs,  461. 
Columbia,  S.  C.,  407. 
Colver,  170,  230. 

Composition,  effect  of  tillage  on,  228. 
Cone,  369. 
Connecticut,  411. 
Constants  for  water,  477. 
Continuous  flow,  for  distribution,  358. 
Continuous  rotation,   for  distribution, 

361 

Cooking  value  of  plants,  228. 
Corbet,  312. 
Corn,  transpiration,  60. 


INDEX 


487 


Corn,  time  of  irrigation,  185. 

protein  in,  221. 

yield  due  to  rainfall,  234. 

under  irrigation,  255. 

cultivation  of,  256. 

yield  with  varying  water,  256. 

time  to  irrigate,  258. 

quantity  of  water  for,  259. 

in  humid  climates,  410,  411. 

early  yield,  457. 
Cotton,  early  yield,  457. 
Council  Bluffs,  454. 
Craigentinny,  415. 
Cranberries,  326. 
Crane,  410. 
Crawley,  29. 
Crop.  See  also  Plant. 

development  under  irrigation,  158. 

time  to  irrigate  short-season  crops, 
183. 

composition,  216. 

use  of  rainfall  in  production,  231. 

value  of  rainfall  in  irrigation,  233. 

tolerance  of  various,  for  alkali,  394. 

yields  under  early  irrigation,  457. 
Crowder,  428. 
Cultivation.    See  also  Mulching. 

saving  water  by,  40. 

against  evaporation,  49. 

time,  53. 

depth,  55. 

frequency,  58. 

and  soil  fertility,  59. 

effect  on  water  use,  121. 

in  dry-farming,  237. 

of  wheat,  243. 

of  corn,  256. 

of  alfalfa,  268. 

of  sugar  beets,  288. 

tools  for,  440. 
Cultivator,    with    shovel    attachment, 

439. 

Cultural  operations,  effect  on  water- 
cost,  141. 
Currants,  326. 

in  humid  climates,  410. 
Cusec  defined,  332. 
Cushman,  106. 

Dammer,  437. 
Danube,  97. 
Date,  314. 

under  irrigation  328. 

alkali-resistant,  396. 
Davis  and  Weber  Counties  Canal,  366, 

378. 
Day  irrigation,  187. 


Dead  Sea,  83. 

Definition  of  irrigation,  4. 

Denver,  408. 

Desert,  rainfall  on,  1. 

Dewberries,  sugar  in,  225,  326. 

Distribution  of  water,  357. 

methods,  358,  361, 364. 

organization  for,  365. 

cost  of,  267. 

regulations  and  records,  368. 
Ditch,  concrete,  197. 

lined,  against  seepage,  376. 

locating,  420,  421. 

permanent,  196. 

typical  farm,  425. 

making,  426. 

discharge  of  various,  432. 
Ditch-tenders,  for  water  distribution, 

367. 

Divisors,  350,  355. 
Dole,  106. 
Dorsey,  403. 
Drainage-water,  composition  of,  78. 

loss  of  plant-food,  79. 

of  wet  lands,  381. 

remedy  for  alkali,  400. 
Drill,  in  sowing  wheat,  242. 
Droughts,  407. 
Dry-farming,  231.   See    also    Rainfall. 

conditions  of,  3. 

mission  of,  7,  231. 

defined,  233. 

results  of,  233. 

cultivation,  237. 

relation  to  irrigation,  237. 

homesteads  for,  238. 

mission  of,  239. 

Congress,  239. 

orchard  experience,  324. 
Dry-matter.  See  also  Water-Cost. 

water-cost  of,  127. 
Duty  of  water  for 

wheat,  248,  252,  253. 

oats,  253. 

barley,  255. 

rye,  255. 

corn,  259. 

rice,  263. 

alfalfa,  274. 

hay  crops,  278. 

clover,  281. 

pastures  and  meadows,  281. 

sugar  beets,  293. 

carrots,  297. 

potatoes,  299. 

peas  and  beans,  301. 

fiber  crops,  305. 


488 


INDEX 


Duty  of  water  for 

hops,  306. 

tomatoes,  306. 

watermelons,  307. 

squash,    307;     pumpkin,   307;    egg- 
plant, 307. 

cantaloupes,  307. 

cabbage,  308. 

cauliflower,  308. 

spinach,308;  lettuce,308;  parsley, 309. 

asparagus,  309;  for  celery,  309. 

onions,  310. 

rhubarb,  310;  tobacco,  310;  peanuts, 
310. 

orchards,  322. 
Duty  of  water. 

defined,  331. 

common  meaning,  332. 

classes  of,  334. 

formula  for,  334. 

difficulty  of  determining,  336. 

and  profit  from  crops,  337. 

cause  of  differences  in,  338. 

in  Africa,  338. 

in  Asia,  339. 

in  Europe,  341. 

in  South  America,  342. 

in  Australia,  343. 

in  North  America,  343. 

under  Bear  River  Canal,  344. 

miscellaneous  results,  345. 

in  Idaho,  345. 

Utah  Station  results,  346. 

the  new  duty,  347. 

in  humid  climates,  413. 

Eaton,  106. 

Economical  irrigation,  wheat,  252. 

against  seepage,  381. 
Edinburgh,  415. 
Eggplant  under  irrigation,  307. 
Egypt,  445,  452. 

duty  of  water  in,  338. 
Elbe,  84. 
Elliot,  403. 
Etcheverry,  329,  403. 
Europe,  duty  of  water  in,  341. 
Evans,  284,  285. 
Evaporation  and  loss  of  soil  moisture,43. 

intensity,  44. 

conditions  determining,  46. 

mulching  against,  49. 

effect  of  rolling,  62. 

conditions  determining  use  of  water 

by  plants,  108. 

Evapo-transpiration  ratio,  132. 
Experiment  stations,  466. 


Factory  waste,  417. 
Fall  irrigation,  175. 

time  of  application,  177. 
Farmers'  Canal,  366. 
Fat  in  plants,  223. 
Fiber  crops  under  irrigation,  305. 
Field-ditch  irrigation,  198. 
Field-lateral  irrigation,  198. 
Field  moisture-capacity,  29. 
Fippin,  13. 
Fitterer,  404. 
Flavor  of  plants,  227. 
Flax  and  alkali,  398. 
Fleming,  403. 
Flour  composition  of,  227. 
Flynn,  369. 

Forage  crops  under  irrigation,  266,278. 
Forbes,  101,  106. 
Fort  Collins,  461. 

Fortier,  46,  48,  49,  63,   156,  215,  239, 
274,  284,  322,  329,  343,  344,  404, 
444,  464,  466,  469. 
Fountain  Colony,  461. 
France,  450,  451. 

duty  of  water  in,  342. 
Free  water,  17. 

Fresno,  alkali  experiment,  402. 
Fruit.  See  also  Orchard. 

composition,  171. 

quality  under  irrigation,  225. 
Fruit-growing.    See  also  Fruits,  Orchard, 

under  irrigation,  314. 
Furrow-irrigation,  207.   See  also  Method 

of  Irrigation. 

Furrowing,  tools  for,  439. 
Fuller,  403. 

Gage  Canal,  366. 

Gain,  162. 

Gallagher,  66,  68,  70,  106. 

Gates  for  ditches,  434. 

Genii,  450. 

Gilbert,  133,  464. 

Gooseberries,  326. 

in  humid  climates,  410. 
Grains.   See  also  Cereals. 

proportion  of  grain,  166. 

time  of  irrigation,  183. 

irrigation  of,  240. 

destiny  of  grain-farming,  241. 

duty  of  water  in  Africa,  339. 
Grant-Mitchell  meter,  442. 
Grapes,  protein  in,  221. 

sugar  in,  225. 

under  irrigation,  327. 
Gray,  471. 
Gravel,  34. 


INDEX 


489 


Greasewood,  397. 
Great  Basin  rivers,  84. 
Great  Britain  rivers,  84. 
Great  Plains,  458. 
Great  Salt  Lake,  83,  389. 

alkali  experiment,  401. 

water,  91. 

Great  Salt  Lake  Valley,  455. 
Greaves,  105,  106,  405. 
Greeley,  457. 
Greeley,  Colo.,  460. 
Green  City,  461. 
Greenhouse  irrigation,  192. 
Green  River,  98. 
Gross  duty  of  water,  335. 
Ground-water,  373. 
Growth,  conditions  of  plant,  130. 
Grubb,  312. 
Guilford,  313. 
Gunnison  River,  96. 

Hammurabi,  446. 

Hanksville,  Utah,  324. 

Hardpan,  30. 

Hare,  106. 

Harris,  146,  156,  172,  187,  264,  405. 

Hawaii,  29, 411. 

Hay,  time  of  irrigation,  186. 

crops  under  irrigation  278. 
Headden,  404. 
Head  of  water,  194. 

proportion  of,  166. 
Hellriegel,  133,  167 
Henry,  7. 
Herrick,  329. 

Hilgard,  20,  106,  239,  393,  398, 404,  466. 
Homesteads  on  dry-farms,  238. 
Hood  River  Valley,  time  of  irrigation 

to,  320. 

Hops  under  irrigation,  306. 
Horton,  369. 
Hirst,  230. 

History  of  irrigation,  445. 
Humbert,  157,  264. 
Humid  climates,  irrigation  in,  406. 

results  of  irrigation  in,  409. 
Hunt,  264. 
Hygroscopic  coefficient,  13. 

Idaho,  time  of  irrigation  in,  320. 

duty  of  water  in,  345. 
Imperial  Valley,  327. 
India,  446,  452. 

duty  of  water  expression,  331. 

duty  of  water  in,  339. 

duty  of  water,  341. 
India  rivers,  84. 


Initial  percentage,  effect  on  evapora- 
tion, 48. 

effect  on  use  by  plants,  111. 
Interculture  of  orchards,  323. 
Irrigation.      See    also    Time,    Method, 
Quantity  of  Irrigation. 

defined,  4,  231. 

conditions,  4. 

extent  of,  5. 

need  of,  5. 

mission  of,  7. 

intermittent  practice,  21. 

response  to,  159. 

supplementary  to  rainfall,  231. 

crop  value  of  rainfall  in,  233. 

relation  to  dry-farming,  237 . 

for  dry-farm  homesteads,  238. 

mission  of,  239. 

engineer  to  measure  water,  349. 

engineer  for  water  distribution,    366. 

in  humid  climates,  406. 

results  in  humid  climates,  409. 

history  of,  445. 

antiquity  of,  445. 

during  Christian  era,  449. 

in  recent  times,  451. 

Congress    in    British    South    Africa, 
453. 

modern  founding  in  America,  454. 

permanent  agriculture  under,  472. 

the  big  problem,  472. 

spirit  of,  473. 

difference   between   arid   and  irriga- 
tion farming,  473. 

history  assures  permanence  of,  474. 

social  condition  of,  476. 

advantages  of,  476. 
Irrigation  Congress,  470. 
Irrigation    Engineer.      See    Irrigation; 

Water  Master. 
Italy,  450. 

duty  of  water  in,  342. 

Java  rivers,  84. 
Johnston,  444. 
Jones,  170,  224,  230. 
Jordan  River,  Utah,  83 
Joseph,  445. 

Kafir  corn,  alkali-resistant,  396. 
Kearney,  387,  392,  404. 
Keeney,  264. 
Kennedy,  341. 
Khankhaje,  156. 
Kiesselbach,  156. 

King,   14,  20,  76,   106,  133,   156,  411, 
415,  418,  476,  484. 


490 


INDEX 


Kneale,  405. 
Knight,  390. 
Kraus,  230,  329. 

Lake  waters,  salinity  of,  86. 
Lateral  organization,  367. 
Lath-boxes,  212. 
Laying-out  farm,  420. 
Lay-off,  440. 

in  furrow  irrigation,  209. 
Lawes,  133. 

Leaching  upward,  81,  385. 
Leather,  39,  133,  134,  136,  156. 
Leaves,  proportion  of,  163. 
Le  Clerc,  230. 

Legumes,  not  alkali-resistant,  398. 
Lemon,  314. 

Lento-capillary  point,  16. 
Lettuce  under  irrigation,  308. 
Leveling  land,  423. 
Lewis,  230,  326,  329. 
Loganberries,  326. 
Lombardy,  450. 

sugar  in,  225. 
Longmont,  461. 
Longyear,  329. 

Loughridge,  30,  39,  215,  392,  393,  404. 
Lucern.  See  Alfalfa. 
Lyman,  352,  369. 
Lyon,  13,  146. 
Lysimeter,  77. 

Macdonald,  239. 

Manager  for  water-distribution,  366. 

Manuring  effect  on  water-use,  121. 

Manufactured  crops, importance  of,  266. 

Marking,  in  furrow  irrigation,  208. 

Mawson,  339. 

Maxwell,  411   418. 

Mayer,  156,  145,  167. 

McClatchie,  179,  188,  239,  404. 

McDowell,  188. 

McLaughlin,  20,  39,  63,  126,  248,  264, 

284,  313. 
McKee,  285. 
Mead,  7,  215,  239,  343,  346,  369,  404, 

418,  464,  466,  468,  484. 
Meadow  hay,  early  yield,  407 
Meadows  under  irrigation,  281 
Means,  404. 
Measurement  of  water.    See  also  Weir. 

Instruments  for,  441. 

need  of,  347. 

classes  of  measurements,  349. 

who  shall  measure,  349. 
Meeker,  460. 
Meheinet  Ali-Pasha,  452. 


Menes,  445. 

Merrill,  188,  215,  265,  239,  285,  313, 

370,  469. 
Meteorology,  effect  on  evaporation,  44, 

47. 
Method  of  irrigation,  189. 

sub-surface  irrigation,  189. 

permanent  ditches,  196. 

open  and  closed  fields,  196. 

field-ditch  or  lateral  method,  198. 

check  method,  202. 

border  method,  202. 

furrow  method,  207. 

basin  method,  207. 

summary  of  methods,  214. 

of  wheat,  243. 

of  alfalfa,  269. 

of  sugar  beets,  289. 

of  orchard,  315. 

in  humid  climates,  412. 
Mexico,  447. 
Milan,  408,  415. 
Mill  waste,  417. 
Mills,  468. 

Mineral  oil,  as  ditch-lining,  377. 
Miner's  inch,  332. 
Mitchell,  106. 
Modules,  350. 

Moisture  in  soil.  See  Soil  Moisture. 
Montgomery,  156. 
Moors,  449. 
Morgan,  146,  157. 
Morgan,  E.  R.,  264,  278,  284,  313. 
Mormon  pioneers,  455,  201. 
Mulching.   See  Cultivation. 

to  check  evaporation,  49. 

self-mulching  soils,  52. 

Nebraska  Station,  37. 

Net  duty  of  water,  335. 

Newell,  7,  346,  369,  462,  464,  484. 

New  England,  406. 

New  Jersey,  410. 

New  Jersey  Station,  469. 

New  Mexico,  alkali  from,  391. 

Night  irrigation,  187. 

Nile,  84,  85,  97,  104,  339,  445. 

Nitrogen.  See  Protein. 

North  America,  duty  of  water  in,  343. 

North  Platte  River,  96. 

Nowell,  264,  313. 

Nursery  stock,  under  irrigation,  326. 

Nuts,  314. 

Oats,  ash  in  leaves,  219. 
ash  in  stalks,  219. 
protein  in,  221. 


INDEX 


491 


Oats,  yield  due  to  rainfall,  234. 

under  irrigation,  253. 

duty  of  water  for,  253. 

early  yield,  457. 
Ocean  water,  91. 

composition,  92. 

Office  of  Experiment  Stations,  464. 
Olin,  484,  285. 

Olive,  duty  of  water  for,  322. 
Omaha,  408. 
Onions  under  irrigation,  310. 

in  humid  climates,  410. 
Orange,  314. 

spacing,  317. 
Orchard.   See  also  Fruit-growing. 

time  of  fall  irrigation,  177. 

time  to  irrigate,  187. 

furrowing,  210. 

under  irrigation,  314. 

method  of  irrigation,  315. 

care  of  young,  315. 

furrows  for  young  trees,  317. 

time  of  irrigation,  319. 

effect  of  irrigation  on  buds,  320. 

quantity  of  water  for,  322. 

danger  of  over-irrigation,  323. 

inter-culture,  323. 

growth  without  irrigation,  324. 

duty  of  water  in  Africa,  339. 
Orchard-grass,  278. 
Organization,  for  distribution,  365. 
Ornamental    Plants    under    irrigation 

328. 

Oshkosb,  Wis.,  407. 
Overfalls,  351. 

Over-irrigation,  371.    See  also  Seepage, 
Alkali. 

delays  ripening,  251. 

danger  in  orchards,  323. 

water-loss  from,  373. 

Packard,  312,  329. 

Packing,  natural,  of  soil,  70. 

Paddock,  329. 

Palestine,  446. 

Palmer,  224. 

Pastures  under  irrigation,  281. 

Patten,  71,  106. 

Peach,  protein  in,  221. 

sugar  in,  225. 

spacing,  317. 
Peanuts,  310. 
Pears,  protein  in,  221. 

spacing,  317. 

duty  of  water  for,  322. 
Peas,  protein  in,  221. 

under  irrigation,  301. 


Pecos  River,  96. 
Pennsylvania,  409. 

Permanence   of   irrigation   agriculture, 
472. 

of  irrigation  assured  by  history,  474. 
Persia,  446. 
Peru,  447. 

duty  of  water  in,  342. 
Peterson,  390. 
Phelps,  411,  418. 
Phoenix,  408. 
Pinckney,  403. 
Plant.   See  also  Crop. 

use  of  soil  moisture  by,  108. 

absorption  of  water  by  plant-roots, 

.    109. 

initial  percentage  and  water  use,  111. 

effect  of  water  distribution  on  water 
use,  114. 

effect  of  time  on  water-use,  115. 

effect  of  soil  depth  on  water  use,  116. 

effect  of  soil  composition  on  water 
use,  117,  118. 

effect  of,  on  water  use,  120. 

rigor  of,  and  water  use,  121. 

effect  of  cultivation  on  water  use,  121. 

effect  of  age  on  water  use,  122. 

effect  of  roots  on  water  use,  122. 

effect  of  kind  on  water  use,  123. 

effect  of  seasons  on  water  use,  123. 

water-cost  of  dry  matter,  127. 

carbon  assimilation,  128. 

age  of,  and  carbon  assimilation,  129. 

conditions  of  growth,  130. 

water-cost  of  several  plants  in  differ- 
ent countries,  133,  134. 

range  of  water-cost,  134. 

effect  of  soil  on  water-cost,  137. 

effect  of  plant-food  on  water  cost,  139. 

effect  of  cultural  operations  on  water- 
cost,  141. 

vigor  of,  and  water-cost,  143. 

water-cost    and    varying    quantities 
of  water,  144. 

nature  of,  and  water-cost,  154. 

development  under  irrigation,  158. 

response  to  irrigation,  159. 

proportion  of  roots,  160. 

proportion  of  leaves  and  stems,  163. 

proportion  of  heads  and  grain,  166. 

proportion  of  parts,  169. 

composition,  216. 

water  in,  217. 

constituents,  217. 

ash  constituents  in,  219. 

protein  in  various,  220, 

fat  in,  223. 


492 


INDEX 


Plant,  carbohydrates  in,  224. 

sugar  in,  224. 

woodiness  in,  226. 

sugar  in,  226. 

color  and  flavor  of,  227. 

cooking  value,  228. 

composition  of  flour,  228. 

tillage  and  composition,  228. 

use  of  rainfall  in  production,  231. 

producing  power  of  rainfall,  232. 

toleration  for  saline  water,  387. 

tolerance  for  alkali,  392. 

tolerance  of  various  plants  for  alkali, 

394. 
Plant-food.    See   also  Ash  constituents. 

loss  by  drainage,  78,  79. 

added  by  water,  87. 

added  by  river  sediments,  101. 

and  water  used  by  planting,  118. 

effect  on  water-cost,  139. 

and  alkali,  390. 

Plowing,  effect  on  water  use,  120. 
Plow,  lateral,  427. 

made  first  irrigation  furrow,  427. 

breaking,  419. 
Plum,  protein  in,  221. 

sugar  in,  225. 
Poplars,  328. 
Potatoes,  ash  in,  219. 

protein  in,  221. 

yield  due  to  rainfall,  234. 

under  irrigation,  298. 

duty  of  water,  344. 

in  humid  climates,  411. 

early  yield,  457. 
Powell,  457,  458,  464,  471. 
Protein,  in  various  plants,  220. 
Prunes,  sugar  in,  225. 
Puddling,  as  ditch-lining,  377. 
Pumpkin  under  irrigation,  307. 

Quantity  of  water  in  one  irrigation,  23. 
Quince,  314. 

Rainfall.  See  also  Dry-farming. 
annual,  1. 
variations,  2. 
seasonal,  2. 
conservation,  3. 
average,  3. 

use  of  in  crop  production,  231. 
irrigation  supplementary  to,  231. 
crop-producing  power,  232. 
crop  value  in  irrigation,  233. 
distribution  of,  235. 
conservation  of,  235. 
types  of,  235. 


Rainfall,  storage  in  soil,  236. 

proportion  conserved,  237. 
Raspberries,  326. 

protein  in,  221. 

in  humid  climates,  410. 
Reclamation  Act,  460. 
Red  River,  96. 
Rees,  230,  329. 

Registers  for  water  measurements,  441. 
Relative  humidity,  effect  on  evapora- 
tion, 47. 

Reservoirs,  seepage  from,  371. 
Response  to  irrigation,  159. 
Rhine,  84,  97. 
Rhubarb,  310. 
Rice,  under  irrigation,  262. 
Richman,  188. 
Ridging,  tools  for,  439. 
Rio  Grande  River,  91,  96. 
Ripening,  delayed  by  over-irrigation, 

251. 

River  water,  salinity  of,  82. 
Riverside,  Cal.,  197. 
Roeding,  290,  313. 
Rolling,  62. 
Roman  Empire,  449. 
Roosevelt,  462. 
Roots,  absorption  of  water  by,  109. 

effect  on  water  use,  122. 

development  in  spring,  182. 

proportion  of,  160. 
Root  crops  under  irrigation,  297. 
Root-hairs,  109. 

Rotation,  method  of  distribution,  361. 
Run-off,  40. 

how  to  prevent,  41. 
Rye,  under  irrigation,  255. 
Rye-grass,  278. 

Sacramento,  408. 

Salt  Lake  City,  78,  455,  470. 

Salt  River,  96. 

Sanborn,  187,  188, 468. 

San  Joaquin  River,  91. 

Saskatchewan  River,  84. 

Schantz,  20. 

Schlichter,  405. 

Schultze,  74. 

Season,  effect  of,  on  water  use,  123. 

time  to  irrigate  short-seaaQd  crops, 
183. 

dry,  407. 
Second-foot,  defined,  331. 

equivalents,  332. 
Sediments,  cracked,  68. 

river,  composition  of,  101. 

physical  effect  on  soil,  102. 


INDEX 


493 


Sediments,  cultural  treatment  of,  103. 

effect  on  crop  yields,  104. 
Seelhorst,  157. 

Seepage.     See  also  Over^irrigation  and 
Alkali. 

from  Indian  canals,  341. 

from  reservoirs  and  canals,  371. 

from  over-irrigation,  373. 

arid  vs.  humid,  375. 

lined  with  ditches  against,  376. 

drainage  against,  381. 

economical  use  of  water  against,  381. 

and  alkali.  384. 
Selina,  Ala.,  407. 
Sevier  River,  375. 
Sewage,  value  in  irrigation,  414. 

use  of,  415. 

Shade,  effect  on  evaporation,  47. 
Shad-scale,  397. 
Shantz,  14,  126,  156. 
Shaw,  239. 
Showers,  59. 

Silting,  as  ditch-lining,  378. 
Slosson,  390. 

Small  fruits,  under  irrigation,  326. 
Smith,  329,  405. 
Smythe,  7,  484. 
Snake  River,  91. 
Snow.  See  also  Rain. 

loss  by  thawing,  41. 
Society  under  irrigation,  476. 
Soil,  size  of  particles,  9. 

composition,  9. 

surface  of  particles,  10. 

moisture  film  of,  11. 

relation  of  particle  and  film,  12. 

hygroscopic  coefficient,  13. 

wilting  coefficient,  14. 

lento-capillary  point,  16. 

maximum  capillary  capacity,  17. 

fill  water  in,  17. 

as  water  reservoir,  21. 

capacity  for  water  of  different,  22. 

unsaturated  under  irrigation,  22. 

field  capacity  of  moisture,  29. 

hardpan  in,  30. 

gravel  in,  34. 

quantity  water  stored  in,  35. 

best  for  irrigation,  35. 

absorption  of  water  by,  38. 

effect  of  evaporation,  47. 

self-mulching,  52. 

fertility  and  cultivation,  59. 

contraction  of,  64. 

changes  due  to  water,  64. 

cohesion  of  particles,  65. 

volume  change,  67. 


Soil,  cracking  of,  68. 

effect  of  water  on  top,  69. 

natural  packing  of,  70. 

successive  wetting  and  drying,  70. 

temperature,  71. 

arid  and  humid  contrasted,  73. 

continuous  solubility,  74. ' 

absorption  by,  76. 

composition  of  drainage  water  from, 
78. 

depth  of  arid,  82. 

plant-food  added  by  water,  93. 

washing  of,  95. 

seasonal  washing  of,  98. 

suspended  matter  added  by  irriga» 
tion,  100. 

suspended  matter  from  surface,  100. 

composition  of  river  sediment,  101. 

physical  effect  of  sediments,  102. 

cultural  treatment  of  sediments,  103. 

water  and  soil  life,  104. 

effect  of  sediments  on  crop  yields,  104. 

effect  of  soil  depth  on  water  use,  116. 

effect  of  composition  on  water  use, 
117,  118. 

effect  on  water-cost,  137. 

storage  of  water  in,  236. 
Soil  fertility  and  cultivation,  59. 
Soil  moisture,  8. 

See  also  Evaporation,     Soil,      Water, 
Water-film,  and  Moisture-film. 

attraction  of  near  bodies,  8. 

film  of,  11. 

relation  of  particle  and  film,  12. 

hygroscopic  coefficient,  13. 

wilting  coefficient,  14. 

lento-capillary  point,  16. 

maximum  capillary  capacity,  17. 

free  water,  17. 

summary,  19. 

soil  as  reservoir,  21. 

capacity  of  different  soils,  22. 

unsaturated  soils  under  irrigation,  22. 

movement  of,  23. 

distribution  of,  25. 

field  capacity,  29. 

effect  of  hardpan,  30. 

distribution  in  furrow  irrigation,  30. 

effect  of  water  table,  34. 

effect  of  gravel,  34. 

quantity  water  stored,  35. 

absorption  by  soils,  38. 

saving  by  cultivation,  40. 

how  disposed  of,  40. 

upward  movement,  42. 

and  evaporation,  43. 

contraction  of  film,  64. 


494 


INDEX 


Soil  moisture,  concentration  of,  79. 

contrasted  with  natural  waters,  87. 

use  of,  by  plants,  108. 

initial  percentage  and  use  by  plants, 
111. 

effect  of  distribution  on  water  use, 
114. 

water-cost  of  dry  matter,  127. 
forghum,  alkali-resistant,  396. 

early  yield,  457. 
South  Africa,  453. 

South  America,  duty  of  water  in,  342. 
South  Dakota,  410. 
Southwestern  Colony,  461. 
Sowing  wheat,  241,  242. 
Spain,  450. 

duty  of  water  in,  342. 
Spinach  under  irrigation,  308. 
Spring  irrigation,  178. 
Springs,  mineral,  salinity  of,  86. 
Squash  under  irrigation,  307. 
Sugar  beets,  152. 

cultural  treatment,  286. 

method  of  irrigation,  289. 
Stabler,  106. 
Stannard,  444. 
Starch  in  plants,  226. 
Strawberries,  protein  in,  221. 
Strawberries,  326. 

sugar  in,  225. 

in  humid  climates,  411. 
Stem,  proportion  of,  163. 
Stewart,  R.,  105,  106,  172,  230, 390,  405. 
Stewart,  Henry,  484. 
St.  Julian  Canal,  450. 
St.  Lawrence  River,  84. 
Storer,  415. 
Storing  Water  in  Soil.    See  Reservoir, 

Soil  and  Soil  Moisture. 
Sub-surface  packer,  62. 
Sub-surface  irrigation,  189. 
Sugar  beets,  time  of  irrigation,  185. 

ash  in,  219. 

protein  in,  221. 

time  to  irrigate,  290. 

quantity  of  water  for,  293. 

duty  of  water,  344. 

alkali-resistant,  396. 
Sugar-cane,  duty  of  water    in  Africa, 
339. 

under  irrigation,  411. 
Sugar  in  plants,  224. 
Superintendent  for  water  distribution, 

366. 

Surface  irrigation,  193. 
Surveys,  water  need  of,  90. 
Suspended  matter.    See  also  Sediments. 


Suspended  matter  in  river  water,  95. 

seasonal  variation  of,  98. 

quantity  added  to  soil,  100. 
Syria,  446. 

Talmage,  405. 

Tannatt,  370,  405. 

Teele,  264,  285,  313,  343,  370,  405,  444. 

Temperature  effect  on  evaporation,  47. 

of  soil,  71. 
Tillage  is  water,  142. 

effect  on  composition,  228. 

against  alkali,  399. 
Time,  a  factor  in  water  use,  115. 
Time  of  irrigation,  29,  173. 

at  lento-capillary  point,  22. 

early  spring  irrigation,  178. 

winter  irrigation,  178. 

irrigation  during  growth,  182. 

short-season  crops,  183. 

long-season  crops,  184. 

frequency  of  irrigation,  185. 

night  vs.  day  irrigation,  187. 

effect  on  composition,  229. 

wheat,  246. 

for  corn,  258. 

of  alfalfa,  270. 

of  sugar  beets,  290. 

for  orchards,  319. 
Timothy,  278. 
Tobacco,  310. 
Tollens,  219,  230. 
Tomato,  171. 

under  irrigation,  306. 
Tools.   See  also  Machines. 

for  irrigation,  419. 
Townsend,  313. 
Transpiration,  110.   See  also  Water-cost. 

water  cost  of  dry  matter,  127. 

water  of  various  plants,  133,  134. 

range  of  ratio,  134. 

effect  of  seasons,  136. 

ratio,  effect  of  soil  on,  137. 

ratio,  denned,  131. 
Transvaal,  339. 
True,  405. 
Tucker,  145,  157. 

Union  Colony,  460. 

United  States,   duty  of  water  expres- 
sion, 331. 

Department  of  Agriculture,  343,  464. 

Bureau  of  Soils,  78,  395,  401. 

Geological  Survey,  442,  457,  464. 

Interior  Department,  463. 

Irrigation  Investigations,  372,  464. 

Office  of  Experiment  Stations,  383. 


INDEX 


495 


United  States  Reclamation  Service, 
370,  461. 

Utah,  alkali  from,  391. 

Utah  Station,  15,  17,  26,  29,  30,  35, 
38,  48,  60,  77,  88,  111,  126,  129, 
136,  142,  146,  154,  159,  165,  166, 
167,  184,  190,  213,  225,  228,  250, 
255,  259,  292,  294,  336,  468,  469. 
duty  of  water  results,  346. 

Utah,  time  of  irrigation  in,  320. 

Valencia  Canal,  450. 
Vineland,  N.  J.,  407. 
Von  Seelhorst,  145. 
Voorhees,  410,  418,  469. 

Walnuts,  spacing,  317. 
Warington,  93. 

Washington,  time  of  irrigation  in,  320. 
Water.    See  also  Soil  moisture,  Rainfall 
and  Snow. 

film,  11. 

soil  as  reservoir,  21. 

how  disposed  of  in  soils,  40. 

soil  changes  due  to,  64. 

cracked  sediments,  68. 

effect  on  top  soil,  69. 

successive  wetting  and  drying,  70. 

universal  solvent,  72. 

continuous  solubility  of  soil,  74. 

composition  of  drainage,  78. 

river,  salinity  of,  82. 

dbmposition  of  river  waters,  84. 

river,  arid  and  humid,  contrasted,  85. 

lake,  salinity  of,  86. 

mineral  springs,  salinity  of,  86. 

natural  and  soil-moisture,  contrasted, 
87. 

plant-food  added  by,  87. 

use  of  concentrated  w.  in  irrigation, 
89. 

surveys,  need  of,  90. 

natural  composition  of,  90,  91. 

natural,  classification  of,  92. 

plant-food  value  of,  93. 

river,  suspended  matter  in,  95. 

seasonal  variation  of  suspended  mat- 
ter, 98. 

suspended  matter  from  surface  soil, 
120. 

suspended  matter  added  to  soil  by, 
100^ 

composition  of  river  sediments,  101. 

and  soil  life,  104. 

effect  of  sediments  on  crop  yields,  104. 

absorption  by  roots,  109. 

tillage  is,  142. 


Water,  cost  and  varying  quantities  of, 
144. 

in  plants,  217. 

quantity  for  wheat,  248. 

storage  in  soil,  236. 

duty,  measurement  and  division,  331. 

units  for  measuring,  332. 

measurement  of,  347. 

distribution  of,  357. 

ground,  374. 

use  of  saline,  387. 

irrigation,     sources     of,     in     humid 
climates,  413. 

conservation     methods     in     humid 
climates,  414. 

constants,  477. 
Water-cost.    See  also  Transpiration. 

of  dry  matter,  127. 

defined,  131. 

of  various  plants,  133,  134. 

range  of  ratio,  134. 

effect  of  seasons,  136. 

effect  of  soil  on,  137. 

effect  of  cultural  operations  in,  141. 

vigor  of  plant  and,  143. 

and  varying  quantities  of  water,  144. 

nature  of  plant  and,  154. 

summary  of  factors,  155. 

of  dry  matter,  232. 
Water-film,  relation  to  particle,  12. 
Water-logging,  drainage  against,  381. 
Water    master.      See    also    Irrigation 
engineer. 

for  water  distribution,  367. 
Watermelons  under  irrigation,  307. 
Waters,  410. 
Water-table,  34. 
Weir,  351. 

rectangular,  351. 

trapezoidal,  352. 

triangular,  352. 

discharge  over  Cippoletti,  478. 
Welch,  188,  234,  265,  285,  313. 
Westgate,  285. 
Wheat,  152,  168. 

protein  in,  221. 

composition  of  flour  from,  228. 

yield  due  to  rainfall,  234. 

spring  vs.  fall,  241. 

quantity  to  sow,  241. 

method  of  sowing,  241,  242. 

method  of  irrigation,  243. 

cultivation  of,  243. 

time  of  irrigation,  246. 

duty  of  water,  248. 

yields  with  varying  water,  250. 

possible  yields  with  water,  252. 


496 


INDEX 


Wheat,  duty  of  water,  344. 

early  yield,  457. 
Wheelon,  253,  344. 
Whipple,  329, 
Whitney,  48,  63. 

Widtsoe,  7,  20,   39,  63,  106,  126,  133, 
134,  157,  172,  188,  215,  230,  239, 
265,  285,  313,  370,  405,  444,  469. 
Wickson,  215,  313,  323,  329. 
Wilcox,  285,  323,  338,  370,  484. 
Willard,  157. 
Williams,  418. 
Wilson,  345,  370. 
Wilting  coefficient,  14. 
Wind,  effect  on  evaporation,  47. 
Wing,  285. 


Winkle,  Van,  106. 

Winsor,  356,  370. 

Winter  irrigation,  178. 

Wollny,  133. 

Woodiness,  in  plants,  226. 

Woodward,  405. 

Wright,  405. 

Wyoming,  duty  of  water  in,  323. 

Wyoming,  alkali  from,  391. 

Wyoming  Station,  303. 

Yield,  effect  of  sediments  on  crop.  104. 

Yoder,  418. 

Young,  Brigham,  454. 

Young,  R.  W.,  470. 


RETURN  TO  the  circulation  desk  of  any 
University  of  California  Library 
or  to  the 

NORTHERN  REGIONAL  LIBRARY  FACILITY 
Bldg.  400,  Richmond  Field  Station 
University  of  California 
Richmond,  CA  94804-4698 

ALL  BOOKS  MAY  BE  RECALLED  AFTER  7  DAYS 
2-month  loans  may  be  renewed  by  calling 

(415)642-6233 
1-year  loans  may  be  recharged  by  bringing  books 

to  NRLF 
Renewals  and  recharges  may  be  made  4  days 

prior  to  due  date 

DUE  AS  STAMPED  BELOW 


AUG9   1988 


1988 


IMTERUBRARYLOAN 


DOT    41989 


UNIV.  OF  CALIF.,  BERK. 


UNIVERSITY  OF  CALIFORNIA  LIBRARY 


